<SEC-DOCUMENT>0001140361-17-044907.txt : 20171204
<SEC-HEADER>0001140361-17-044907.hdr.sgml : 20171204
<ACCEPTANCE-DATETIME>20171204173943
ACCESSION NUMBER:		0001140361-17-044907
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20171128
FILED AS OF DATE:		20171204
DATE AS OF CHANGE:		20171204

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Mahmood Nabeel
		CENTRAL INDEX KEY:			0001723975

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-32897
		FILM NUMBER:		171238086

	MAIL ADDRESS:	
		STREET 1:		2126 INYO STREET
		CITY:			FRESNO
		STATE:			CA
		ZIP:			93721

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			UNITED SECURITY BANCSHARES
		CENTRAL INDEX KEY:			0001137547
		STANDARD INDUSTRIAL CLASSIFICATION:	NATIONAL COMMERCIAL BANKS [6021]
		IRS NUMBER:				912112732
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2126 INYO STREET
		CITY:			FRESNO
		STATE:			CA
		ZIP:			93721
		BUSINESS PHONE:		5592484930

	MAIL ADDRESS:	
		STREET 1:		2126 INYO STREET
		CITY:			FRESNO
		STATE:			CA
		ZIP:			93721
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

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

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001137547</issuerCik>
        <issuerName>UNITED SECURITY BANCSHARES</issuerName>
        <issuerTradingSymbol>UBFO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001723975</rptOwnerCik>
            <rptOwnerName>Mahmood Nabeel</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2126 INYO STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FRESNO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>93721</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>UBFO COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Mr. Mahmood has no equity ownership in UBFO.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/S/ Nabeel Mahmood</signatureName>
        <signatureDate>2017-12-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
