<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

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

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001121783</issuerCik>
        <issuerName>AMERICAN SPECTRUM REALTY INC</issuerName>
        <issuerTradingSymbol>AQQ</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001167472</rptOwnerCik>
            <rptOwnerName>GALARDI JOHN N</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4440 VON KARMAN AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 222</rptOwnerStreet2>
            <rptOwnerCity>NEWPORT BEACH</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92660</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>18.25</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-05-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1250</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-05-05</value>
            </exerciseDate>
            <expirationDate>
                <value>2016-05-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1250</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>103018</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The option to buy common stock vests in four equal installments with the first installment vesting on the date of grant.</footnote>
        <footnote id="F2">Represents 6,250 stock options and 96,768 shares of the Issuer's common stock which are benefically owned via ownership of 387,073 Operating Partnership Units (OP Units) in the American Spectrum Realty Operating Partnership, L.P.  Each four OP Units are exchangable for cash (equal to fair market value of the Issuer's common stock) or at the Issuer's option, one share of the Issuer's common stock.  Of the OP Units reported as owned, 382,537 are owned by Meadow Wood Village, Ltd, an entity in which the undersigned owns a significant interest.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John N Galardi</signatureName>
        <signatureDate>2006-05-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
