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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 pXVxoducHkyLZZRoiDxYgQ==

<SEC-DOCUMENT>0000874977-08-000036.txt : 20080401
<SEC-HEADER>0000874977-08-000036.hdr.sgml : 20080401
<ACCEPTANCE-DATETIME>20080401140850
ACCESSION NUMBER:		0000874977-08-000036
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20070507
FILED AS OF DATE:		20080401
DATE AS OF CHANGE:		20080401

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			State Auto Financial CORP
		CENTRAL INDEX KEY:			0000874977
		STANDARD INDUSTRIAL CLASSIFICATION:	FIRE, MARINE & CASUALTY INSURANCE [6331]
		IRS NUMBER:				311324304
		STATE OF INCORPORATION:			OH
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		518 EAST BROAD STREET
		CITY:			COLUMBUS
		STATE:			OH
		ZIP:			43215
		BUSINESS PHONE:		6144645000

	MAIL ADDRESS:	
		STREET 1:		518 EAST BROAD STREET
		CITY:			COLUMBUS
		STATE:			OH
		ZIP:			43215

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	STATE AUTO FINANCIAL CORP
		DATE OF NAME CHANGE:	19930328

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Baker Robert Ellison
		CENTRAL INDEX KEY:			0001398593

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19289
		FILM NUMBER:		08728620

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		614-464-5000

	MAIL ADDRESS:	
		STREET 1:		518 EAST BROAD STREET
		CITY:			COLUMBUS
		STATE:			OH
		ZIP:			43215
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-05-07</periodOfReport>

    <issuer>
        <issuerCik>0000874977</issuerCik>
        <issuerName>State Auto Financial CORP</issuerName>
        <issuerTradingSymbol>STFC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001398593</rptOwnerCik>
            <rptOwnerName>Baker Robert Ellison</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1310 GLEN CEDARS DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MABLETON</rptOwnerCity>
            <rptOwnerState>GA</rptOwnerState>
            <rptOwnerZipCode>30126</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares without par value</value>
            </securityTitle>
            <transactionDate>
                <value>2007-05-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>300</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>30.05</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1726.808</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes restricted share units (RSUs) credited with dividends, equivalent in value to those declared and paid on one share of STFC common stock; 1,400.00 shares acquired on 5/4/07; 4.494 shares acquired on 6/29/07; 7.027 shares acquired on 9/28/07; 7.764 shares acquired on 12/28/07 and 7.523 shares acquired on 3/31/08.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert E. Baker by James A. Yano, attorney in fact pursuant to a POA filed with the Commission 5-8-07</signatureName>
        <signatureDate>2008-04-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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