<SUBMISSION>
<ACCESSION-NUMBER>0001127602-09-016151
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20090724
<FILING-DATE>20090727
<DATE-OF-FILING-DATE-CHANGE>20090727
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>Brenzia John N
<CIK>0001288942
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-12508
<FILM-NUMBER>09964683
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>309 MAIN STREET
<CITY>IRWIN
<STATE>PA
<ZIP>15642
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>S&T BANCORP INC
<CIK>0000719220
<ASSIGNED-SIC>6022
<IRS-NUMBER>251434426
<STATE-OF-INCORPORATION>PA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>800 PHILADELPHIA STREET
<STREET2>PO BOX 190
<CITY>INDIANA
<STATE>PA
<ZIP>15701
<PHONE>7244651466
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>800 PHILADELPHIA STREET
<STREET2>PO BOX 190
<CITY>INDIANA
<STATE>PA
<ZIP>15701
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-07-24</periodOfReport>

    <issuer>
        <issuerCik>0000719220</issuerCik>
        <issuerName>S&amp;T BANCORP INC</issuerName>
        <issuerTradingSymbol>STBA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001288942</rptOwnerCik>
            <rptOwnerName>Brenzia John N</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>800 PHILADELPHIA STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>INDIANA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-07-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.95</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10469</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Wendy S. Bell P.O.A. for John N. Brenzia</signatureName>
        <signatureDate>2009-07-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
