<SUBMISSION>
<ACCESSION-NUMBER>0001021465-07-000002
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20071206
<FILING-DATE>20071212
<DATE-OF-FILING-DATE-CHANGE>20071212
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>ON ASSIGNMENT INC
<CIK>0000890564
<ASSIGNED-SIC>7363
<IRS-NUMBER>954023433
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>26651 WEST AGOURA ROAD
<CITY>CALABASAS
<STATE>CA
<ZIP>91302
<PHONE>8188787900
</BUSINESS-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>PIERCE EDWARD L
<CIK>0001021465
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-20540
<FILM-NUMBER>071302786
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>4400 POST OAK PARKWAY
<STREET2>STE 1130
<CITY>HOUSTON
<STATE>TX
<ZIP>77027
<PHONE>7139613633
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET2>4400 POST OAK PKWY SUITE 1130
<CITY>HOUSTON
<STATE>TX
<ZIP>77027
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgardoc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-12-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000890564</issuerCik>
        <issuerName>ON ASSIGNMENT INC</issuerName>
        <issuerTradingSymbol>ASGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001021465</rptOwnerCik>
            <rptOwnerName>PIERCE EDWARD L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ON ASSIGNMENT, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>26651 WEST AGOURA ROAD</rptOwnerStreet2>
            <rptOwnerCity>CALABASAS</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91302</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.41</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-12-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>18000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-12-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This option vest in thirds on the anniversary of grant date over a three year period.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Power of Attorney, James Brill, CFO  For: Edward L. Pierce</signatureName>
        <signatureDate>2007-12-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
