-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 PMvhtM2J/6uFQJhYbJz2aK2favI420tLKg78r4xtYxnQnUBjSdRQ35UXecvlGrAO
 gE1Bsvi9PUhCsQqOXp5fvw==

<SEC-DOCUMENT>0001140361-03-004427.txt : 20031121
<SEC-HEADER>0001140361-03-004427.hdr.sgml : 20031121
<ACCEPTANCE-DATETIME>20031121143312
ACCESSION NUMBER:		0001140361-03-004427
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20031121
FILED AS OF DATE:		20031121

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FOSTER LEE B II
		CENTRAL INDEX KEY:			0001215495

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-10436
		FILM NUMBER:		031017736

	BUSINESS ADDRESS:	
		STREET 1:		C/O L B FOSTER CO
		STREET 2:		415 HOLIDAY DRIVE
		CITY:			PITTSBURGH
		STATE:			PA
		ZIP:			15220
		BUSINESS PHONE:		4129287842

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			FOSTER L B CO
		CENTRAL INDEX KEY:			0000352825
		STANDARD INDUSTRIAL CLASSIFICATION:	WHOLESALE-METALS SERVICE CENTERS & OFFICES [5051]
		IRS NUMBER:				251324733
		STATE OF INCORPORATION:			PA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		415 HOLIDAY DR
		CITY:			PITTSBURGH
		STATE:			PA
		ZIP:			15220
		BUSINESS PHONE:		4129283431

	MAIL ADDRESS:	
		STREET 1:		415 HOLIDAY DR
		CITY:			PITTSBURGH
		STATE:			PA
		ZIP:			15220
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-11-21</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000352825</issuerCik>
        <issuerName>FOSTER L B CO</issuerName>
        <issuerTradingSymbol>fstr</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001215495</rptOwnerCik>
            <rptOwnerName>FOSTER LEE B II</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>L.B. FOSTER COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>415 HOLIDAY DRIVE</rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15220</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Chairman</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable>
<nonDerivativeTransaction>
<securityTitle>
<value>Common Stock</value>
</securityTitle>
<transactionDate>
<value>2003-11-24</value>
</transactionDate>
<deemedExecutionDate>
</deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>M</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionTimeliness>
<value></value>
</transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>0</value>
</transactionShares>
<transactionPricePerShare>
<value>3.56</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode>
<value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>0</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeTransaction>
<nonDerivativeTransaction>
<securityTitle>
<value>Common Stock</value>
</securityTitle>
<transactionDate>
<value>2003-11-21</value>
</transactionDate>
<deemedExecutionDate>
</deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>S</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionTimeliness>
<value></value>
</transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>5000</value>
</transactionShares>
<transactionPricePerShare>
<value>6.104</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode>
<value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>162800</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>5000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value>By Foster Holdings Retirement Savings Plan a 401(k) plan.</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding>
<securityTitle>
<value>Common Stock</value>
</securityTitle>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>19800</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value>By Children</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding>
<securityTitle>
<value>Common Stock</value>
</securityTitle>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>25754</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value>Approximate share equivalent to units held in 401(k) trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable>
<derivativeHolding>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>4.38</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>1998-10-23</value>
</exerciseDate>
<expirationDate>
<value>2008-10-23</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>32500</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>32500</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>4.44</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2000-03-01</value>
</exerciseDate>
<expirationDate>
<value>2010-02-28</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>100000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>100000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>2.75</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2001-02-02</value>
</exerciseDate>
<expirationDate>
<value>2011-02-01</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>20000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>20000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>3.65</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2001-05-09</value>
</exerciseDate>
<expirationDate>
<value>2011-05-08</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>30000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>30000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>5.50</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2002-05-15</value>
</exerciseDate>
<expirationDate>
<value>2012-05-14</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>10000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>10000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeTransaction>
<securityTitle>
<value>Option to Buy</value>
</securityTitle>
<conversionOrExercisePrice>
<value>3.56</value>
</conversionOrExercisePrice>
<transactionDate>
<value>2003-11-21</value>
</transactionDate>
<deemedExecutionDate>
</deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>M</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionTimeliness>
<value></value>
</transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>5000</value>
</transactionShares>
<transactionPricePerShare>
<value>3.56</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode>
<value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<exerciseDate>
<value>1994-07-22</value>
</exerciseDate>
<expirationDate>
<value>2004-07-21</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>5000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>23600</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeTransaction>
</derivativeTable>
<remarks></remarks>
<ownerSignature>
<signatureName>Lee B. Foster II</signatureName>
<signatureDate>2003-11-21</signatureDate>
</ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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