-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 K9fowOMavBme+XXlG07mJQ==

<SEC-DOCUMENT>0001044321-08-000165.txt : 20080424
<SEC-HEADER>0001044321-08-000165.hdr.sgml : 20080424
<ACCEPTANCE-DATETIME>20080424105357
ACCESSION NUMBER:		0001044321-08-000165
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080422
FILED AS OF DATE:		20080424
DATE AS OF CHANGE:		20080424

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			PECO II INC
		CENTRAL INDEX KEY:			0000845072
		STANDARD INDUSTRIAL CLASSIFICATION:	CONSTRUCTION SPECIAL TRADE CONTRACTORS [1700]
		IRS NUMBER:				341605456
		STATE OF INCORPORATION:			OH
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1376 STATE ROUTE 598
		CITY:			GALION
		STATE:			OH
		ZIP:			44833
		BUSINESS PHONE:		4194687600

	MAIL ADDRESS:	
		STREET 1:		1376 STATE ROUTE 598
		CITY:			GALION
		STATE:			OH
		ZIP:			44833

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MARXE AUSTIN W & GREENHOUSE DAVID M
		CENTRAL INDEX KEY:			0001044321

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-31283
		FILM NUMBER:		08773463

	BUSINESS ADDRESS:	
		STREET 1:		C/O SPECIAL SITUATIONS FUNDS
		STREET 2:		527 MADISON AVENUE, SUITE 2600
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10022
		BUSINESS PHONE:		2122076500

	MAIL ADDRESS:	
		STREET 1:		C/O SPECIAL SITUATIONS FUNDS
		STREET 2:		527 MADISON AVENUE, SUITE 2600
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10022
</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>2008-04-22</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000845072</issuerCik>
        <issuerName>PECO II INC</issuerName>
        <issuerTradingSymbol>PIII</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001044321</rptOwnerCik>
            <rptOwnerName>MARXE AUSTIN W &amp; GREENHOUSE DAVID M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SPECIAL SITUATIONS FUNDS</rptOwnerStreet1>
            <rptOwnerStreet2>527 MADISON AVENUE, SUITE 2600</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-04-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.4706</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3202718</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Limited Partnerships</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse).  They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP) and Special Situations Cayman Fund, L.P. (Cayman), respectively. 2,178,212 shares of Common Stock are held by QP and 1,024,506 shares of Common Stock are held by Cayman. The interest of Marxe and Greenhouse in the shares of Common Stock owned by QP and Cayman is limited to the extent of his pecuniary interest.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Austin W. Marxe</signatureName>
        <signatureDate>2008-04-24</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>David M. Greenhouse</signatureName>
        <signatureDate>2008-04-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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