<PAGE>
      AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JUNE 13, 2003

                                                      REGISTRATION NO. 333-

================================================================================


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                   ----------

                             RELIANT RESOURCES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

                  DELAWARE                            76-0655566
        (State or Other Jurisdiction of            (I.R.S. Employer
        Incorporation or Organization)             Identification No.)

                              1111 LOUISIANA STREET
                              HOUSTON, TEXAS 77002
                    (Address of Principal Executive Offices)


                             RELIANT RESOURCES, INC.
                          EMPLOYEE STOCK PURCHASE PLAN
                            (Full Title of the Plan)


                                MICHAEL L. JINES
                    SENIOR VICE PRESIDENT AND GENERAL COUNSEL
                              1111 LOUISIANA STREET
                              HOUSTON, TEXAS 77002
                     (Name and Address of Agent for Service)
   Telephone Number, Including Area Code, of Agent for Service: (713) 497-3000

                                   ----------

                         CALCULATION OF REGISTRATION FEE

<Table>
<Caption>
                                                                  PROPOSED MAXIMUM     PROPOSED MAXIMUM
           TITLE OF SECURITIES                 AMOUNT TO BE      OFFERING PRICE PER    AGGREGATE OFFERING        AMOUNT OF
            TO BE REGISTERED                    REGISTERED           SHARE (1)              PRICE (1)         REGISTRATION FEE
-----------------------------------------   ------------------   ------------------    ------------------    ------------------
<S>                                         <C>                  <C>                   <C>                   <C>
Common Stock, $.001 par value ...........    15,000,000 shares   $             6.31    $    94,650,000.00    $         7,658.00
Preferred Stock Purchase Rights(2) ......    15,000,000 rights                   (3)                   (3)                   (3)
</Table>

(1)   Estimated solely for the purpose of calculating the registration fee in
      accordance with Rule 457(c) based upon the average of the high and low
      prices of the Common Stock of Reliant Resources, Inc. reported on the New
      York Stock Exchange Composite Tape on June 11, 2003.
(2)   Each share of Common Stock to be registered includes one associated
      Preferred Stock Purchase Right.
(3)   No separate consideration is payable for the Preferred Stock Purchase
      Rights. Therefore, the registration fee for such securities is included in
      the registration fee for the Common Stock.

================================================================================


<PAGE>

                             INTRODUCTORY STATEMENT

         Reliant Resources, Inc. (the "Registrant" or the "Company") has
previously filed a Registration Statement on Form S-8 relating to its Common
Stock, par value $.001 per share, and associated rights to purchase its Series A
Preferred Stock, par value $.001 per share (such common stock and associated
rights are collectively referred to in this Registration Statement as the
"Common Stock"), issuable pursuant to the terms of the Reliant Resources, Inc.
2002 Stock Plan. Pursuant to General Instruction E of Form S-8, this
Registration Statement covers additional securities registered for issuance
under the Reliant Resources, Inc. 2002 Stock Plan. The contents of the prior
Registration Statement on Form S-8 (333-86610) of the Company relating to such
plan are incorporated herein by reference.


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed with the Commission by the Company
pursuant to the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), or as otherwise indicated, are hereby incorporated in this Registration
Statement by reference as of their respective dates:

                  (1) the Company's Amendment to Annual Report on Form 10-K/A
for the fiscal year ended December 31, 2002, filed May 1, 2003 as updated by
financial information included in the Current Report on Form 8-K filed on
June 5, 2003;

                  (2) all other documents filed by the Company pursuant to
Section 13(a), 14 or 15(d) of the Exchange Act since December 31, 2002; and

                  (3) the description of the Common Stock contained in the
Company's Registration Statement on Form 8-A, as filed with the Commission on
April 27, 2001 pursuant to the Exchange Act, as amended by Amendment No. 1
thereto on Form 8-A/A, as filed with the Commission on May 1, 2001.

         All documents filed with the Commission by the Company pursuant to
Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of
this Registration Statement and prior to the filing of a post-effective
amendment to this Registration Statement which indicates that all securities
offered hereby 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 incorporated by reference herein
shall be deemed to be modified or superseded for purposes of this Registration
Statement to the extent that a statement contained herein or in any subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any statement so modified or superseded
shall not be deemed, except as so modified or superseded, to constitute a part
of this Registration Statement.


<PAGE>

ITEM 8.  EXHIBITS.

         The following documents are filed as a part of this Registration
Statement:

EXHIBIT
5.1  -       Opinion of Skadden, Arps, Slate, Meagher & Flom LLP

23.1 -       Consent of Deloitte & Touche LLP

23.2 -       Consent of Skadden, Arps, Slate, Meagher & Flom LLP (included in
             Exhibit 5.1)

24.1 -       Power of Attorney (included on the signature page to this
             Registration Statement)


<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 Houston, the State of Texas, on June 13, 2003.

                                     RELIANT RESOURCES, INC.
                                     (Registrant)


                                     By:   /s/ Joel V. Staff
                                           ----------------------------------
                                           Joel V. Staff,
                                           Chairman and Chief Executive Officer


                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Joel V. Staff and Michael L. Jines, and
each of them severally, his or her true and lawful attorney or attorneys-in-fact
and agents, with full power to act with or without the others and with full
power of substitution and resubstitution, to execute in his or her name place
and stead, in any and all capacities, any or all amendments (including
pre-effective and post-effective amendments) to this Registration Statement and
any registration statement for the same offering filed pursuant to Rule 462
under the Securities Act of 1933, as amended, and to file the same, with all
exhibits thereto, and other documents in connection therewith, with the
Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents and each of them full power and authority, to do and perform in the name
and on behalf of the undersigned, in any and all capacities, each and every act
and thing necessary or desirable to be done in and about the premises, to all
intents and purposes and as fully as they might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents or their
substitutes may lawfully 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 dates indicated.

<Table>
<Caption>
          SIGNATURE                                  TITLE                                DATE
          ---------                                  -----                                ----
<S>                                    <C>                                            <C>


       /s/ Joel V. Staff                        Chairman, Chief                       June 13, 2003
--------------------------------        Executive Officer and Director
        (Joel V. Staff)                (Principal Executive Officer and
                                                  Director)


      /s/ Mark M. Jacobs                    Executive Vice President                  June 13, 2003
--------------------------------          and Chief Financial Officer
       (Mark M. Jacobs)                  (Principal Financial Officer)


    /s/ Thomas C. Livengood                   Vice President and                      June 13, 2003
--------------------------------        Controller (Principal Accounting
     (Thomas C. Livengood)                        Officer)
</Table>


<PAGE>

<Table>
<Caption>
<S>                                    <C>                                            <C>
/s/ E. William Barnett                            Director                            June 13, 2003
--------------------------------
      (E. William Barnett)


/s/ Donald J. Breeding                            Director                            June 13, 2003
--------------------------------
       (Donald J. Breeding)


/s/ Laree E. Perez                                Director                            June 13, 2003
--------------------------------
       (Laree E. Perez)


/s/ William L. Transier                           Director                            June 13, 2003
--------------------------------
        (William L. Transier)
</Table>


<PAGE>

                                INDEX TO EXHIBITS

<Table>
<Caption>
EXHIBIT
<S>      <C>
5.1      Opinion of Skadden, Arps, Slate, Meagher & Flom LLP

23.1     Consent of Deloitte & Touche LLP

23.2     Consent of Skadden, Arps, Slate, Meagher & Flom LLP (included in
         Exhibit 5.1)

24.1     Power of Attorney (included on the signature page to this Registration
         Statement)
</Table>
[{"type": "S-8", "sequence": "1", "filename": "h06729bsv8.txt", "description": "RELIANT RESOURCES, INC. - EMP. STOCK PURCHASE PLAN", "secsgml_size_bytes": 11485}]
{"company-data": {"conformed-name": "RELIANT RESOURCES INC", "cik": "0001126294", "assigned-sic": "4911", "irs-number": "760655566", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-106098", "film-number": "03743475"}, "business-address": {"street1": "RELIANT ENERGY INC", "street2": "1111 LOUISIANA STREET", "city": "HOUSTON", "state": "TX", "zip": "77002", "phone": "7132073000"}}
AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JUNE 13, 2003

                                                      REGISTRATION NO. 333-

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                   ----------

                             RELIANT RESOURCES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

                  DELAWARE                            76-0655566
        (State or Other Jurisdiction of            (I.R.S. Employer
        Incorporation or Organization)             Identification No.)

                              1111 LOUISIANA STREET
                              HOUSTON, TEXAS 77002
                    (Address of Principal Executive Offices)

                             RELIANT RESOURCES, INC.
                          EMPLOYEE STOCK PURCHASE PLAN
                            (Full Title of the Plan)

                                MICHAEL L. JINES
                    SENIOR VICE PRESIDENT AND GENERAL COUNSEL
                              1111 LOUISIANA STREET
                              HOUSTON, TEXAS 77002
                     (Name and Address of Agent for Service)
   Telephone Number, Including Area Code, of Agent for Service: (713) 497-3000

                                   ----------

                         CALCULATION OF REGISTRATION FEE
PROPOSED MAXIMUM     PROPOSED MAXIMUM
           TITLE OF SECURITIES                 AMOUNT TO BE      OFFERING PRICE PER    AGGREGATE OFFERING        AMOUNT OF
            TO BE REGISTERED                    REGISTERED           SHARE (1)              PRICE (1)         REGISTRATION FEE
-----------------------------------------   ------------------   ------------------    ------------------    ------------------
Common Stock, $.001 par value ...........    15,000,000 shares   $             6.31    $    94,650,000.00    $         7,658.00
Preferred Stock Purchase Rights(2) ......    15,000,000 rights                   (3)                   (3)                   (3)
(1)   Estimated solely for the purpose of calculating the registration fee in
      accordance with Rule 457(c) based upon the average of the high and low
      prices of the Common Stock of Reliant Resources, Inc. reported on the New
      York Stock Exchange Composite Tape on June 11, 2003.
(2)   Each share of Common Stock to be registered includes one associated
      Preferred Stock Purchase Right.
(3)   No separate consideration is payable for the Preferred Stock Purchase
      Rights. Therefore, the registration fee for such securities is included in
      the registration fee for the Common Stock.

================================================================================
INTRODUCTORY STATEMENT

         Reliant Resources, Inc. (the "Registrant" or the "Company") has
previously filed a Registration Statement on Form S-8 relating to its Common
Stock, par value $.001 per share, and associated rights to purchase its Series A
Preferred Stock, par value $.001 per share (such common stock and associated
rights are collectively referred to in this Registration Statement as the
"Common Stock"), issuable pursuant to the terms of the Reliant Resources, Inc.
2002 Stock Plan. Pursuant to General Instruction E of Form S-8, this
Registration Statement covers additional securities registered for issuance
under the Reliant Resources, Inc. 2002 Stock Plan. The contents of the prior
Registration Statement on Form S-8 (333-86610) of the Company relating to such
plan are incorporated herein by reference.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed with the Commission by the Company
pursuant to the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), or as otherwise indicated, are hereby incorporated in this Registration
Statement by reference as of their respective dates:

                  (1) the Company's Amendment to Annual Report on Form 10-K/A
for the fiscal year ended December 31, 2002, filed May 1, 2003 as updated by
financial information included in the Current Report on Form 8-K filed on
June 5, 2003;

                  (2) all other documents filed by the Company pursuant to
Section 13(a), 14 or 15(d) of the Exchange Act since December 31, 2002; and

                  (3) the description of the Common Stock contained in the
Company's Registration Statement on Form 8-A, as filed with the Commission on
April 27, 2001 pursuant to the Exchange Act, as amended by Amendment No. 1
thereto on Form 8-A/A, as filed with the Commission on May 1, 2001.

         All documents filed with the Commission by the Company pursuant to
Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of
this Registration Statement and prior to the filing of a post-effective
amendment to this Registration Statement which indicates that all securities
offered hereby 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 incorporated by reference herein
shall be deemed to be modified or superseded for purposes of this Registration
Statement to the extent that a statement contained herein or in any subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any 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.

         The following documents are filed as a part of this Registration
Statement:

EXHIBIT
5.1  -       Opinion of Skadden, Arps, Slate, Meagher & Flom LLP

23.1 -       Consent of Deloitte & Touche LLP

23.2 -       Consent of Skadden, Arps, Slate, Meagher & Flom LLP (included in
             Exhibit 5.1)

24.1 -       Power of Attorney (included on the signature page to this
             Registration Statement)
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 Houston, the State of Texas, on June 13, 2003.

                                     RELIANT RESOURCES, INC.
                                     (Registrant)

                                     By:   /s/ Joel V. Staff
                                           ----------------------------------
                                           Joel V. Staff,
                                           Chairman and Chief Executive Officer

                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Joel V. Staff and Michael L. Jines, and
each of them severally, his or her true and lawful attorney or attorneys-in-fact
and agents, with full power to act with or without the others and with full
power of substitution and resubstitution, to execute in his or her name place
and stead, in any and all capacities, any or all amendments (including
pre-effective and post-effective amendments) to this Registration Statement and
any registration statement for the same offering filed pursuant to Rule 462
under the Securities Act of 1933, as amended, and to file the same, with all
exhibits thereto, and other documents in connection therewith, with the
Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents and each of them full power and authority, to do and perform in the name
and on behalf of the undersigned, in any and all capacities, each and every act
and thing necessary or desirable to be done in and about the premises, to all
intents and purposes and as fully as they might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents or their
substitutes may lawfully 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 dates indicated.
SIGNATURE                                  TITLE                                DATE
          ---------                                  -----                                ----
/s/ Joel V. Staff                        Chairman, Chief                       June 13, 2003
--------------------------------        Executive Officer and Director
        (Joel V. Staff)                (Principal Executive Officer and
                                                  Director)

      /s/ Mark M. Jacobs                    Executive Vice President                  June 13, 2003
--------------------------------          and Chief Financial Officer
       (Mark M. Jacobs)                  (Principal Financial Officer)

    /s/ Thomas C. Livengood                   Vice President and                      June 13, 2003
--------------------------------        Controller (Principal Accounting
     (Thomas C. Livengood)                        Officer)
/s/ E. William Barnett                            Director                            June 13, 2003
--------------------------------
      (E. William Barnett)

/s/ Donald J. Breeding                            Director                            June 13, 2003
--------------------------------
       (Donald J. Breeding)

/s/ Laree E. Perez                                Director                            June 13, 2003
--------------------------------
       (Laree E. Perez)

/s/ William L. Transier                           Director                            June 13, 2003
--------------------------------
        (William L. Transier)
INDEX TO EXHIBITS
EXHIBIT
5.1      Opinion of Skadden, Arps, Slate, Meagher & Flom LLP

23.1     Consent of Deloitte & Touche LLP

23.2     Consent of Skadden, Arps, Slate, Meagher & Flom LLP (included in
         Exhibit 5.1)

24.1     Power of Attorney (included on the signature page to this Registration
         Statement)