<SEC-DOCUMENT>0001562180-21-000144.txt : 20210106
<SEC-HEADER>0001562180-21-000144.hdr.sgml : 20210106
<ACCEPTANCE-DATETIME>20210106085653
ACCESSION NUMBER:		0001562180-21-000144
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210104
FILED AS OF DATE:		20210106
DATE AS OF CHANGE:		20210106

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Vasista Vittal
		CENTRAL INDEX KEY:			0001652827

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-37553
		FILM NUMBER:		21509121

	MAIL ADDRESS:	
		STREET 1:		C/O REGENXBIO INC.
		STREET 2:		9600 BLACKWELL ROAD, SUITE 210
		CITY:			ROCKVILLE
		STATE:			MD
		ZIP:			20850

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			REGENXBIO Inc.
		CENTRAL INDEX KEY:			0001590877
		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
		IRS NUMBER:				471851754
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		9600 BLACKWELL ROAD
		STREET 2:		SUITE 210
		CITY:			ROCKVILLE
		STATE:			MD
		ZIP:			20850
		BUSINESS PHONE:		240-552-8181

	MAIL ADDRESS:	
		STREET 1:		9600 BLACKWELL ROAD
		STREET 2:		SUITE 210
		CITY:			ROCKVILLE
		STATE:			MD
		ZIP:			20850

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	REGENXBIO, Inc.
		DATE OF NAME CHANGE:	20150116

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ReGenX Biosciences, LLC
		DATE OF NAME CHANGE:	20131101
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primarydocument.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-01-04</periodOfReport>

    <notSubjectToSection16>false</notSubjectToSection16>

    <issuer>
        <issuerCik>0001590877</issuerCik>
        <issuerName>REGENXBIO Inc.</issuerName>
        <issuerTradingSymbol>RGNX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001652827</rptOwnerCik>
            <rptOwnerName>Vasista Vittal</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O REGENXBIO INC.</rptOwnerStreet1>
            <rptOwnerStreet2>9600 BLACKWELL ROAD, SUITE 210</rptOwnerStreet2>
            <rptOwnerCity>ROCKVILLE</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>20850</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>false</isDirector>
            <isOfficer>true</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-01-04</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>12400.00</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>145424.00</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>44.97</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2021-01-04</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>56200.00</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2031-01-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>56200.00</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>56200.00</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 1, 2022, January 1, 2023, January 1, 2024 and January 1, 2025 while the recipient provides continuous service to the Issuer.</footnote>
        <footnote id="F2">25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 4, 2022 while the optionee provides continuous service to the Issuer.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Patrick J. Christmas as attorney-in-fact</signatureName>
        <signatureDate>2021-01-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
