-----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,
 M/TkUONTFI1tqiVf52gj/0CM+7F/rYPCPw8vWLx9pNCFtM0ir20URJKggeZLjCye
 Kv/QCe1DhkxQzDeH7HuisQ==

<SEC-DOCUMENT>0001179110-06-011231.txt : 20060517
<SEC-HEADER>0001179110-06-011231.hdr.sgml : 20060517
<ACCEPTANCE-DATETIME>20060517174106
ACCESSION NUMBER:		0001179110-06-011231
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060512
FILED AS OF DATE:		20060517
DATE AS OF CHANGE:		20060517

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ZENITH NATIONAL INSURANCE CORP
		CENTRAL INDEX KEY:			0000109261
		STANDARD INDUSTRIAL CLASSIFICATION:	FIRE, MARINE & CASUALTY INSURANCE [6331]
		IRS NUMBER:				952702776
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		21255 CALIFA ST
		CITY:			WOODLAND HILLS
		STATE:			CA
		ZIP:			91367
		BUSINESS PHONE:		8187131000

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ROTHENBERG ALAN I
		CENTRAL INDEX KEY:			0001238629

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-09627
		FILM NUMBER:		06850021

	MAIL ADDRESS:	
		STREET 1:		633 WEST FIFTH ST.
		STREET 2:		SUITE 4000
		CITY:			LOS ANGELES
		STATE:			CA
		ZIP:			90071
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-05-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000109261</issuerCik>
        <issuerName>ZENITH NATIONAL INSURANCE CORP</issuerName>
        <issuerTradingSymbol>ZNT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238629</rptOwnerCik>
            <rptOwnerName>ROTHENBERG ALAN I</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1ST CENTURY BANK, N.A.</rptOwnerStreet1>
            <rptOwnerStreet2>1875 CENTURY PARK EAST, SUITE 1450</rptOwnerStreet2>
            <rptOwnerCity>LOS ANGELES</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90067</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-05-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>38.97</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>52.80</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>38.97</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7388.22</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each share of phantom stock is a deferred stock unit payable only in cash and is the economic equivalent of a share of the Issuer's common stock.</footnote>
        <footnote id="F2">Deferred stock units become payable upon the Reporting Person's termination of service as a director and are payable only in cash (not in stock) in a lump sum or in installments over five or ten years at the Reporting Person's election made at the time of the deferral.  Earlier distribution of all or part of the deferred stock units may also be elected if such early distribution is after 24 months from the Reporting Person's election to defer his compensation into deferred stock units.</footnote>
        <footnote id="F3">Dividends on Common Stock deemed received and reinvested in deferred stock units.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Alan I. Rothenberg</signatureName>
        <signatureDate>2006-05-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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