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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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<SEC-DOCUMENT>0001255452-07-000001.txt : 20070820
<SEC-HEADER>0001255452-07-000001.hdr.sgml : 20070820
<ACCEPTANCE-DATETIME>20070820132711
ACCESSION NUMBER:		0001255452-07-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20070820
FILED AS OF DATE:		20070820
DATE AS OF CHANGE:		20070820

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Flaherty & Crumrine PREFERRED INCOME OPPORTUNITY FUND INC
		CENTRAL INDEX KEY:			0000882071
		IRS NUMBER:				954355600
		STATE OF INCORPORATION:			MD
		FISCAL YEAR END:			1130

	BUSINESS ADDRESS:	
		STREET 1:		301 E COLORADO BLVD STE 720
		STREET 2:		C/O FLAHERTY & CRUMRINE INC
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91101
		BUSINESS PHONE:		(626) 795-7300

	MAIL ADDRESS:	
		STREET 1:		301 COLORADO BLVD STE 720
		STREET 2:		C/O FLAHERTY & CRUMRINE INC
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91101

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	PREFERRED INCOME OPPORTUNITY FUND INC
		DATE OF NAME CHANGE:	19920929

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			STONE BRADFORD S
		CENTRAL INDEX KEY:			0001255452

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	811-06495
		FILM NUMBER:		071067244

	BUSINESS ADDRESS:	
		STREET 1:		FLAHERTY & CRUMRINE INC
		STREET 2:		392 SPRINGFIELD AVE MEZZANINE SUITE
		CITY:			SUMMIT
		STATE:			NJ
		ZIP:			07901
		BUSINESS PHONE:		9089180300

	MAIL ADDRESS:	
		STREET 1:		392 SPRINGFIELD AVE MEZZANINE SUITE
		CITY:			SUMMIT
		STATE:			NJ
		ZIP:			07901
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-08-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000882071</issuerCik>
        <issuerName>Flaherty &amp; Crumrine PREFERRED INCOME OPPORTUNITY FUND INC</issuerName>
        <issuerTradingSymbol>PFO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001255452</rptOwnerCik>
            <rptOwnerName>STONE BRADFORD S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>392 SPRINGFIELD AVE MEZZANINE SUITE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SUMMIT</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-08-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Mr. Stone also indirectly holds an additional 8,603 shares of the Fund through his ownership of 10% of Flaherty &amp; Crumrine Incorporated</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Bradford S. Stone</signatureName>
        <signatureDate>2007-08-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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