<SEC-DOCUMENT>0001475246-17-000020.txt : 20171130
<SEC-HEADER>0001475246-17-000020.hdr.sgml : 20171130
<ACCEPTANCE-DATETIME>20171130170731
ACCESSION NUMBER:		0001475246-17-000020
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20171128
FILED AS OF DATE:		20171130
DATE AS OF CHANGE:		20171130

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Marcotte Robert L
		CENTRAL INDEX KEY:			0001374463

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	814-00237
		FILM NUMBER:		171231830

	MAIL ADDRESS:	
		STREET 1:		1100 WILSON BOULEVARD, SUITE 3000
		CITY:			ARLINGTON
		STATE:			VA
		ZIP:			22209

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GLADSTONE CAPITAL CORP
		CENTRAL INDEX KEY:			0001143513
		IRS NUMBER:				542040781
		STATE OF INCORPORATION:			MD
		FISCAL YEAR END:			0930

	BUSINESS ADDRESS:	
		STREET 1:		1521 WESTBRANCH DRIVE
		STREET 2:		SUITE 100
		CITY:			MCLEAN
		STATE:			VA
		ZIP:			22102
		BUSINESS PHONE:		703-287-5800

	MAIL ADDRESS:	
		STREET 1:		1521 WESTBRANCH DRIVE
		STREET 2:		SUITE 100
		CITY:			MCLEAN
		STATE:			VA
		ZIP:			22102
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-11-28</periodOfReport>

    <issuer>
        <issuerCik>0001143513</issuerCik>
        <issuerName>GLADSTONE CAPITAL CORP</issuerName>
        <issuerTradingSymbol>GLAD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001374463</rptOwnerCik>
            <rptOwnerName>Marcotte Robert L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1521 WESTBRANCH DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 100</rptOwnerStreet2>
            <rptOwnerCity>MCLEAN</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-11-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4329</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.79</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>381770</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-11-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3671</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.85</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>385441</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The price reporded in column 4 is a weighted average price. These shares were purchased in multiple transactions ranging from $9.7833 to $9.8000 inclusive. The reporting person undertakes to provide to Gladstone Capital Corporation, any security holder of Gladstone Capital Corporation, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.</footnote>
        <footnote id="F2">The price reporded in column 4 is a weighted average price. These shares were purchased in multiple transactions ranging from $9.8404 to $9.8499 inclusive. The reporting person undertakes to provide to Gladstone Capital Corporation, any security holder of Gladstone Capital Corporation, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Michael LiCalsi, Attorney-in-fact</signatureName>
        <signatureDate>2017-11-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
