<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-05-19</periodOfReport>
    <issuer>
        <issuerCik>0001008554</issuerCik>
        <issuerName>HUMBOLDT BANCORP</issuerName>
        <issuerTradingSymbol>HBEK</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001102039</rptOwnerCik>
            <rptOwnerName>MASON THEODORE S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-05-19</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>3000</value></transactionShares><transactionValue><value>13.1018</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>81624</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>I</value><footnoteId id="F1"/></natureOfOwnership></ownershipNature></nonDerivativeSecurity><footnotes><footnote id="F1">Breakdown of Common Stock Owned: 290 shares held By Immediate Family Member, 16,055 shares held By Self via D.A. Davidson &amp;amp; Co., 65,279 shares held By Self.</footnote></footnotes><ownerSignature><signatureName>Theodore S. Mason</signatureName><signatureDate>2003-05-19</signatureDate></ownerSignature><ownerSignature><signatureName>Signed by Patrick J. Rusnak, Power of Attorney on File</signatureName><signatureDate>2003-05-19</signatureDate></ownerSignature></ownershipDocument>

