-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 F2molX0LtQBdjTfyHmXoPLSwlGyV2P9EkLe8YDzbXJkr/d/xxPloL46ht7ugp58G
 9d60CVKJfnZgymi3sABJ8Q==

<SEC-DOCUMENT>0001140361-05-006762.txt : 20050825
<SEC-HEADER>0001140361-05-006762.hdr.sgml : 20050825
<ACCEPTANCE-DATETIME>20050825161934
ACCESSION NUMBER:		0001140361-05-006762
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050817
FILED AS OF DATE:		20050825
DATE AS OF CHANGE:		20050825

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Townsend Vance Todd
		CENTRAL INDEX KEY:			0001336333

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-18859
		FILM NUMBER:		051049104

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		405-225-5224

	MAIL ADDRESS:	
		STREET 1:		300 JOHNNY BENCH DRIVE
		CITY:			OKLAHOMA CITY
		STATE:			OK
		ZIP:			73104

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SONIC CORP
		CENTRAL INDEX KEY:			0000868611
		STANDARD INDUSTRIAL CLASSIFICATION:	RETAIL-EATING PLACES [5812]
		IRS NUMBER:				731371046
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0831

	BUSINESS ADDRESS:	
		STREET 1:		300 JOHNNY BENCH DRIVE
		CITY:			OKLAHOMA CITY
		STATE:			OK
		ZIP:			73104
		BUSINESS PHONE:		4052255000

	MAIL ADDRESS:	
		STREET 1:		300 JOHNNY BENCH DRIVE
		STREET 2:		4TH FLOOR
		CITY:			OKLAHOMA CITY
		STATE:			OK
		ZIP:			73104
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2005-08-17</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000868611</issuerCik>
        <issuerName>SONIC CORP</issuerName>
        <issuerTradingSymbol>SONC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001336333</rptOwnerCik>
            <rptOwnerName>Townsend Vance Todd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>300 JOHNNY BENCH DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OKLAHOMA CITY</rptOwnerCity>
            <rptOwnerState>OK</rptOwnerState>
            <rptOwnerZipCode>73104</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President and CMO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.61</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2008-08-17</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-08-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>30000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">One-third of the options vest on each of the first three anniversary dates following the date of grant.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Vance Todd Townsend</signatureName>
        <signatureDate>2005-08-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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