-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 AaM7b8xMisZAGhgDJ8o2wiIk6PLZJ5rYY70TX57Yw8Yd29fl5Nvg+J8tgbPtYj+E
 h6mc+EfsQRu7hHPg4eXuiQ==

<SEC-DOCUMENT>0001143513-10-000005.txt : 20100510
<SEC-HEADER>0001143513-10-000005.hdr.sgml : 20100510
<ACCEPTANCE-DATETIME>20100510094431
ACCESSION NUMBER:		0001143513-10-000005
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100507
FILED AS OF DATE:		20100510
DATE AS OF CHANGE:		20100510

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Mead Gerard
		CENTRAL INDEX KEY:			0001346826

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	814-00237
		FILM NUMBER:		10814487

	MAIL ADDRESS:	
		STREET 1:		1521 WESTBRANCH DRIVE
		STREET 2:		SUITE 200
		CITY:			MCLEAN
		STATE:			VA
		ZIP:			22102

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
		CITY:			MCLEAN
		STATE:			VA
		ZIP:			22102
		BUSINESS PHONE:		703-287-5851

	MAIL ADDRESS:	
		STREET 1:		1521 WESTBRANCH DRIVE
		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>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-05-07</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001346826</rptOwnerCik>
            <rptOwnerName>Mead Gerard</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GLADSTONE CAPITAL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>1521 WESTBRANCH DRIVE #200</rptOwnerStreet2>
            <rptOwnerCity>MCLEAN</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-05-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>100</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2825.0468</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Paula Novara, attorney-in-fact</signatureName>
        <signatureDate>2010-05-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----