<PAGE>

    As filed with the Securities and Exchange Commission on January 31, 2003

                          Registration No. 333- _______
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                             MERCATOR SOFTWARE, INC.
             (Exact name of registrant as specified in its charter)

                Delaware                                  06-1132156
     (State or other jurisdiction of                   (I.R.S. Employer
     incorporation or organization)                   Identification No.)

                                 45 Danbury Road
                            Wilton, Connecticut 06897
               (Address of Principal Executive Offices) (Zip Code)

                          ----------------------------

                           1997 Equity Incentive Plan
                            (Full title of the plan)

                          ----------------------------

                              David L. Goret, Esq.
                                 General Counsel
                             Mercator Software, Inc.
                                 45 Danbury Road
                            Wilton, Connecticut 06897
                                 (203) 761-8600
             (Name, address including zip code and telephone number,
                   including area code, of agent for service)

                          ----------------------------

                                   Copies to:
                               Paul A. Soden, Esq.
                                THOMPSON HINE LLP
                            One Chase Manhattan Plaza
                            New York, New York 10005
                                 (212) 344-5680

================================================================================
                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------
    Title of                                                      Proposed maximum
securities to be      Amount to be        Proposed maximum       aggregate offering       Amount of
   registered          registered      offering price per unit          price         registration fee
---------------------------------------------------------------------------------------------------------
<S>                   <C>              <C>                       <C>                  <C>
Common stock, $0.01    2,589,642 (1)          $1.725 (2)            $4,467,132.45           $414.00
par value
---------------------------------------------------------------------------------------------------------
</TABLE>

<PAGE>

(1) Upon the filing and effectiveness of this Registration Statement on Form
S-8, the total number of shares of Common Stock registered pursuant to the 1997
Equity Incentive Plan will be 14,789,642 plus such additional shares as may be
required pursuant to the plan in the event of a stock dividend, split-up of
shares, recapitalization or other similar change in the Common Stock.

(2) Estimated, in accordance with Rule 457(c) and (h)(1) of Regulation C of the
Securities Act, the price of $1.725 per share, is the average of the high and
low prices of the Common Stock as reported on The Nasdaq National Market on
January 27, 2003, and is set forth solely for purposes of calculating the filing
fee for those shares without a fixed exercise price.

                                Explanatory Note

         This Registration Statement, on Form S-8, is being filed by Mercator
Software, Inc. (the "Company" or "Registrant") with the Securities and Exchange
Commission (the "SEC") pursuant to General Instruction E on Form S-8 for the
purpose of registering under the Securities Act, as amended (the "Act")
2,589,642 additional shares of Common Stock, par value $0.01 per share, of the
Company ("Common Stock") for issuance pursuant to the Company's 1997 Equity
Incentive Plan.

         The Company has heretofore registered under the Act a total of
12,200,000 shares of Common Stock for issuance under the Company's 1997 Equity
Incentive Plan by means of the currently effective Registration Statements on
Form S-8 (Registration No. 333-37969, 333-89951, 333-32002, 333-59240, 333-73432
and 333-97349) previously filed with the SEC (the "Prior Registration
Statements").

         The contents of the Prior Registration Statements are hereby
incorporated by reference into this Registration Statement.

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

     The following documents of the Registrant which have been filed with the
SEC pursuant to the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), are incorporated in this Registration Statement by reference as of their
respective dates:

     (a) The Registrant's Annual Report on Form 10-K for the fiscal year ended
December 31, 2001, filed with the SEC on March 18, 2002;

     (b) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended March 31, 2002 filed with the SEC on May 15, 2002;

     (c) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended June 30, 2002 filed with the SEC on August 14, 2002;

     (d) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended September 30, 2002 filed with the SEC on November 13, 2002; and

     (e) "Description of Registrant's Securities to be Registered" contained in
the Registrant's registration statement on Form 8-A filed with the SEC on June
6, 1997 pursuant to Section 12(g) of the Exchange Act and incorporating by
reference the information contained in the Registrant's Registration Statement
on Form S-1 (SEC File No. 333-27293) initially filed with the Commission on
March 6, 1997 as amended.

<PAGE>

     All documents subsequently filed with the SEC by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all securities offered herein
have been sold or which deregisters all securities then remaining unsold, shall
be deemed to be incorporated by reference in this Registration Statement and to
be a part hereof from the date of filing of such documents.

         Any statement contained herein or in a document incorporated or deemed
to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes hereof to the extent that a statement contained herein
or in any other subsequently filed document which is also incorporated or deemed
to be incorporated by reference herein modifies or supersedes such statement.
Any such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.

Item 8. Exhibits.

   Exhibit No.               Description of Exhibit
4.1                   Amended and Restated Certificate of Incorporation, as
                      amended, of the Registrant (filed as Exhibit 3.1 to the
                      Registrant's Quarterly Report on Form 10-Q on November 14,
                      2000, File No. 000-22667 (7674707), and incorporated by
                      reference herein).*

4.2                   Amended and Restated By-Laws of the Registrant (filed as
                      Exhibit 3.1 to the Registrant's Registration Statement on
                      Form 8-A on September 4, 1998, File No. 000-22667
                      (98704715), and incorporated by reference herein).*

4.3                   1997 Equity Incentive Plan, as amended, of the Registrant
                      (filed as Exhibit 10.37 to the Registrant's Quarterly
                      Report on Form 10-Q on August 14, 2002, File No. 000-22667
                      and incorporated by reference herein).*

5.1                   Opinion of David L. Goret, Esq. **

23.1                  Consent of David L. Goret, Esq. (contained in his opinion
                      as Exhibit 5.1).

23.2                  Consent of KPMG LLP. **

24.1                  Power of Attorney (included as part of the signature page
                      of this Registration Statement).

     *Not filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.

<PAGE>

                                  SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Wilton, the State of Connecticut, on this 31st day of
January, 2003.

                     MERCATOR SOFTWARE, INC.


                     By: /s/ Roy C. King
                         -----------------------------------------------
                         Roy C. King
                         Chairman of the Board of Directors, Chief Executive
                         Officer and President

                               POWER OF ATTORNEY

     EACH SUCH PERSON WHOSE SIGNATURE appears below constitutes and appoints,
jointly and severally, Roy C. King and Kenneth J. Hall and each of them, with
full power to act without the other, his true and lawful attorney-in-fact and
agent, with the power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8 (including post-effective amendments) and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, hereby ratifying and
confirming all that said attorney-in-fact, or his or her substitute or
substitutes, may do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.

<TABLE>
<CAPTION>
Signature                             Title                             Date
<S>                                   <C>                               <C>
PRINCIPAL EXECUTIVE OFFICER
AND DIRECTOR

/s/ Roy C. King                       Chairman of the Board of          January 31, 2003
--------------------------            Directors, Chief Executive
Roy C. King                           Officer and President

PRINCIPAL FINANCIAL AND
PRINCIPAL ACCOUNTING OFFICER

/s/  Kenneth J. Hall                  Executive Vice President,         January 31, 2003
--------------------------            Chief Financial Officer and
Kenneth J. Hall                       Treasurer
</TABLE>

<PAGE>

Additional Directors:


/s/ Constance F. Galley
-------------------------
Constance F. Galley


/s/ Ernest E. Keet
-------------------------
Ernest E. Keet


/s/ Michael E. Lehman
-------------------------
Michael E. Lehman


/s/ James P. Schadt
-------------------------
James P. Schadt


/s/ Dennis G. Sisco
-------------------------
Dennis G. Sisco


/s/ Mark C. Stevens
-------------------------
Mark C. Stevens

<PAGE>

                                INDEX TO EXHIBITS


  Exhibit                 Description of Exhibit
  -------                 ----------------------

4.1             Amended and Restated Certificate of Incorporation, as amended,
                of the Registrant (filed as Exhibit 3.1 to the Registrant's
                Quarterly Report on Form 10-Q on November 14, 2000, File
                No. 000-22667 (7674707), and incorporated by reference herein).*

4.2             Amended and Restated By-Laws of the Registrant (filed as Exhibit
                3.1 to the Registrant's Registration Statement on Form 8-A on
                September 4, 1998, File No. 000-22667 (98704715), and
                incorporated by reference herein).*

4.3             1997 Equity Incentive Plan, as amended, of the Registrant (filed
                as Exhibit 10.37 to the Registrant's Quarterly Report on Form
                10-Q on August 14, 2002, File No. 000-22667 and incorporated by
                reference herein).*

5.1             Opinion of David L. Goret, Esq. **

23.1            Consent of David L. Goret, Esq. (contained in his opinion as
                Exhibit 5.1).

23.2            Consent of KPMG LLP.**

24.1            Power of Attorney (included as part of the signature page of
                this Registration Statement).


     *Not filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.
[{"type": "S-8", "sequence": "1", "filename": "ds8.txt", "description": "FORM S-8 -- 1997 EQUITY INCENTIVE PLAN", "secsgml_size_bytes": 13302}]
{"company-data": {"conformed-name": "MERCATOR SOFTWARE INC", "cik": "0001039276", "assigned-sic": "7372", "irs-number": "061132156", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-102899", "film-number": "03535146"}, "business-address": {"street1": "45 DANBURY RD", "city": "WILTON", "state": "CT", "zip": "06897", "phone": "2037617600"}, "mail-address": {"street1": "45 DANBURY", "city": "WILTON", "state": "CT", "zip": "06897"}, "former-company": {"former-conformed-name": "TSI INTERNATIONAL SOFTWARE LTD", "date-changed": "19970514"}}
As filed with the Securities and Exchange Commission on January 31, 2003

                          Registration No. 333- _______
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                             MERCATOR SOFTWARE, INC.
             (Exact name of registrant as specified in its charter)

                Delaware                                  06-1132156
     (State or other jurisdiction of                   (I.R.S. Employer
     incorporation or organization)                   Identification No.)

                                 45 Danbury Road
                            Wilton, Connecticut 06897
               (Address of Principal Executive Offices) (Zip Code)

                          ----------------------------

                           1997 Equity Incentive Plan
                            (Full title of the plan)

                          ----------------------------

                              David L. Goret, Esq.
                                 General Counsel
                             Mercator Software, Inc.
                                 45 Danbury Road
                            Wilton, Connecticut 06897
                                 (203) 761-8600
             (Name, address including zip code and telephone number,
                   including area code, of agent for service)

                          ----------------------------

                                   Copies to:
                               Paul A. Soden, Esq.
                                THOMPSON HINE LLP
                            One Chase Manhattan Plaza
                            New York, New York 10005
                                 (212) 344-5680

================================================================================
                         CALCULATION OF REGISTRATION FEE
---------------------------------------------------------------------------------------------------------
    Title of                                                      Proposed maximum
securities to be      Amount to be        Proposed maximum       aggregate offering       Amount of
   registered          registered      offering price per unit          price         registration fee
---------------------------------------------------------------------------------------------------------
Common stock, $0.01    2,589,642 (1)          $1.725 (2)            $4,467,132.45           $414.00
par value
---------------------------------------------------------------------------------------------------------
(1) Upon the filing and effectiveness of this Registration Statement on Form
S-8, the total number of shares of Common Stock registered pursuant to the 1997
Equity Incentive Plan will be 14,789,642 plus such additional shares as may be
required pursuant to the plan in the event of a stock dividend, split-up of
shares, recapitalization or other similar change in the Common Stock.

(2) Estimated, in accordance with Rule 457(c) and (h)(1) of Regulation C of the
Securities Act, the price of $1.725 per share, is the average of the high and
low prices of the Common Stock as reported on The Nasdaq National Market on
January 27, 2003, and is set forth solely for purposes of calculating the filing
fee for those shares without a fixed exercise price.

                                Explanatory Note

         This Registration Statement, on Form S-8, is being filed by Mercator
Software, Inc. (the "Company" or "Registrant") with the Securities and Exchange
Commission (the "SEC") pursuant to General Instruction E on Form S-8 for the
purpose of registering under the Securities Act, as amended (the "Act")
2,589,642 additional shares of Common Stock, par value $0.01 per share, of the
Company ("Common Stock") for issuance pursuant to the Company's 1997 Equity
Incentive Plan.

         The Company has heretofore registered under the Act a total of
12,200,000 shares of Common Stock for issuance under the Company's 1997 Equity
Incentive Plan by means of the currently effective Registration Statements on
Form S-8 (Registration No. 333-37969, 333-89951, 333-32002, 333-59240, 333-73432
and 333-97349) previously filed with the SEC (the "Prior Registration
Statements").

         The contents of the Prior Registration Statements are hereby
incorporated by reference into this Registration Statement.

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

     The following documents of the Registrant which have been filed with the
SEC pursuant to the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), are incorporated in this Registration Statement by reference as of their
respective dates:

     (a) The Registrant's Annual Report on Form 10-K for the fiscal year ended
December 31, 2001, filed with the SEC on March 18, 2002;

     (b) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended March 31, 2002 filed with the SEC on May 15, 2002;

     (c) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended June 30, 2002 filed with the SEC on August 14, 2002;

     (d) The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
ended September 30, 2002 filed with the SEC on November 13, 2002; and

     (e) "Description of Registrant's Securities to be Registered" contained in
the Registrant's registration statement on Form 8-A filed with the SEC on June
6, 1997 pursuant to Section 12(g) of the Exchange Act and incorporating by
reference the information contained in the Registrant's Registration Statement
on Form S-1 (SEC File No. 333-27293) initially filed with the Commission on
March 6, 1997 as amended.
All documents subsequently filed with the SEC by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all securities offered herein
have been sold or which deregisters all securities then remaining unsold, shall
be deemed to be incorporated by reference in this Registration Statement and to
be a part hereof from the date of filing of such documents.

         Any statement contained herein or in a document incorporated or deemed
to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes hereof to the extent that a statement contained herein
or in any other subsequently filed document which is also incorporated or deemed
to be incorporated by reference herein modifies or supersedes such statement.
Any such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.

Item 8. Exhibits.

   Exhibit No.               Description of Exhibit
4.1                   Amended and Restated Certificate of Incorporation, as
                      amended, of the Registrant (filed as Exhibit 3.1 to the
                      Registrant's Quarterly Report on Form 10-Q on November 14,
                      2000, File No. 000-22667 (7674707), and incorporated by
                      reference herein).*

4.2                   Amended and Restated By-Laws of the Registrant (filed as
                      Exhibit 3.1 to the Registrant's Registration Statement on
                      Form 8-A on September 4, 1998, File No. 000-22667
                      (98704715), and incorporated by reference herein).*

4.3                   1997 Equity Incentive Plan, as amended, of the Registrant
                      (filed as Exhibit 10.37 to the Registrant's Quarterly
                      Report on Form 10-Q on August 14, 2002, File No. 000-22667
                      and incorporated by reference herein).*

5.1                   Opinion of David L. Goret, Esq. **

23.1                  Consent of David L. Goret, Esq. (contained in his opinion
                      as Exhibit 5.1).

23.2                  Consent of KPMG LLP. **

24.1                  Power of Attorney (included as part of the signature page
                      of this Registration Statement).

     *Not filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.
SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Wilton, the State of Connecticut, on this 31st day of
January, 2003.

                     MERCATOR SOFTWARE, INC.

                     By: /s/ Roy C. King
                         -----------------------------------------------
                         Roy C. King
                         Chairman of the Board of Directors, Chief Executive
                         Officer and President

                               POWER OF ATTORNEY

     EACH SUCH PERSON WHOSE SIGNATURE appears below constitutes and appoints,
jointly and severally, Roy C. King and Kenneth J. Hall and each of them, with
full power to act without the other, his true and lawful attorney-in-fact and
agent, with the power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8 (including post-effective amendments) and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, hereby ratifying and
confirming all that said attorney-in-fact, or his or her substitute or
substitutes, may do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.
Signature                             Title                             Date
PRINCIPAL EXECUTIVE OFFICER
AND DIRECTOR

/s/ Roy C. King                       Chairman of the Board of          January 31, 2003
--------------------------            Directors, Chief Executive
Roy C. King                           Officer and President

PRINCIPAL FINANCIAL AND
PRINCIPAL ACCOUNTING OFFICER

/s/  Kenneth J. Hall                  Executive Vice President,         January 31, 2003
--------------------------            Chief Financial Officer and
Kenneth J. Hall                       Treasurer
Additional Directors:

/s/ Constance F. Galley
-------------------------
Constance F. Galley

/s/ Ernest E. Keet
-------------------------
Ernest E. Keet

/s/ Michael E. Lehman
-------------------------
Michael E. Lehman

/s/ James P. Schadt
-------------------------
James P. Schadt

/s/ Dennis G. Sisco
-------------------------
Dennis G. Sisco

/s/ Mark C. Stevens
-------------------------
Mark C. Stevens
INDEX TO EXHIBITS

  Exhibit                 Description of Exhibit
  -------                 ----------------------

4.1             Amended and Restated Certificate of Incorporation, as amended,
                of the Registrant (filed as Exhibit 3.1 to the Registrant's
                Quarterly Report on Form 10-Q on November 14, 2000, File
                No. 000-22667 (7674707), and incorporated by reference herein).*

4.2             Amended and Restated By-Laws of the Registrant (filed as Exhibit
                3.1 to the Registrant's Registration Statement on Form 8-A on
                September 4, 1998, File No. 000-22667 (98704715), and
                incorporated by reference herein).*

4.3             1997 Equity Incentive Plan, as amended, of the Registrant (filed
                as Exhibit 10.37 to the Registrant's Quarterly Report on Form
                10-Q on August 14, 2002, File No. 000-22667 and incorporated by
                reference herein).*

5.1             Opinion of David L. Goret, Esq. **

23.1            Consent of David L. Goret, Esq. (contained in his opinion as
                Exhibit 5.1).

23.2            Consent of KPMG LLP.**

24.1            Power of Attorney (included as part of the signature page of
                this Registration Statement).

     *Not filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.