<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001346164</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001590877</issuerCik>
            <issuerName>REGENXBIO INC</issuerName>
            <secFileNumber>001-37553</secFileNumber>
            <issuerAddress>
                <ns2:street1>9804 Medical Center Drive </ns2:street1>
                <ns2:city>Rockville</ns2:city>
                <ns2:stateOrCountry>MD</ns2:stateOrCountry>
                <ns2:zipCode>20850</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>2405528181</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>CURRAN M SIMPSON</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Director</relationshipToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>8th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>25106</noOfUnitsSold>
            <aggregateMarketValue>359768.98</aggregateMarketValue>
            <noOfUnitsOutstanding>49255966</noOfUnitsOutstanding>
            <approxSaleDate>07/29/2024</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>12/09/2019</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock Units</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>25106</amountOfSecuritiesAcquired>
            <paymentDate>12/09/2019</paymentDate>
            <natureOfPayment>N/A</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <remarks>The securities to be sold were acquired upon the vesting of restricted stock units during the period of 12/09/2019 through 01/01/2024.
</remarks>
        <noticeSignature>
            <noticeDate>07/29/2024</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>03/15/2024</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Curran M Simpson</signature>
        </noticeSignature>
    </formData>
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144
0001346164
XXXXXXXX
LIVE
0001590877
REGENXBIO INC
001-37553
9804 Medical Center Drive
Rockville
MD
20850
2405528181
CURRAN M SIMPSON
Director
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
8th Floor
New York
NY
10004
25106
359768.98
49255966
07/29/2024
NASDAQ
Common
12/09/2019
Restricted Stock Units
Issuer
N
25106
12/09/2019
N/A
Y
The securities to be sold were acquired upon the vesting of restricted stock units during the period of 12/09/2019 through 01/01/2024.
07/29/2024
03/15/2024
/s/ Curran M Simpson