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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 FdjozBxkLqiMdgSq6tj/QnUiUESsslJkLWpWMfNgkda4hCJ0SD22SgsqCPwd2xo2
 UJIc7EnNScQGUYBvqGX6mA==

<SEC-DOCUMENT>0000950138-06-000592.txt : 20060731
<SEC-HEADER>0000950138-06-000592.hdr.sgml : 20060731
<ACCEPTANCE-DATETIME>20060731161246
ACCESSION NUMBER:		0000950138-06-000592
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060727
FILED AS OF DATE:		20060731
DATE AS OF CHANGE:		20060731

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MKS INSTRUMENTS INC
		CENTRAL INDEX KEY:			0001049502
		STANDARD INDUSTRIAL CLASSIFICATION:	INDUSTRIAL INSTRUMENTS FOR MEASUREMENT, DISPLAY, AND CONTROL [3823]
		IRS NUMBER:				042277512
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		90 INDUSTRIAL WAY
		CITY:			WILMINGTON
		STATE:			MA
		ZIP:			01887
		BUSINESS PHONE:		978-284-4000

	MAIL ADDRESS:	
		STREET 1:		90 INDUSTRIAL WAY
		CITY:			WILMINGTON
		STATE:			MA
		ZIP:			01887

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EMERSON ELECTRIC CO
		CENTRAL INDEX KEY:			0000032604
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRONIC & OTHER ELECTRICAL EQUIPMENT (NO COMPUTER EQUIP) [3600]
		STATE OF INCORPORATION:			MO
		FISCAL YEAR END:			0930

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-23621
		FILM NUMBER:		06991266

	BUSINESS ADDRESS:	
		STREET 1:		8000 W FLORISSANT AVE
		STREET 2:		P O BOX 4100
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63136
		BUSINESS PHONE:		3145532000

	MAIL ADDRESS:	
		STREET 1:		8000 W. FLORISSANT
		STREET 2:		P.O. BOX 4100
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63136

	FORMER NAME:	
		FORMER CONFORMED NAME:	EMERSON ELECTRIC MANUFACTUING CO
		DATE OF NAME CHANGE:	19730710
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4_072806ex.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-07-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001049502</issuerCik>
        <issuerName>MKS INSTRUMENTS INC</issuerName>
        <issuerTradingSymbol>MKSI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000032604</rptOwnerCik>
            <rptOwnerName>EMERSON ELECTRIC CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>8000 W. FLORISSANT AVE.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ST LOUIS</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63136</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>2006-07-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>25000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.8127</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5178474</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Through a subsidiary</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-07-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>25000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.2385</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5153474</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Through a subsidiary</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1065182</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The sales were effected in multiple transactions, at varying prices, on July 27, 2006, as follows and as described in
 Footnotes 2 and 3 below: 100 shares at $19.68; 200 at $19.79; 100 at $19.95; 200 at $20.22; 100 at $20.23; 100 at $20.24;
 168 at $20.26; 200 at $20.36; 200 at $20.47; 100 at $20.49; 200 at $20.58; 200 at $20.60; 100 at $20.64; 200 at $20.69; 300
 at $20.7; 200 at $20.74; 400 at $20.79; 100 at $20.80; 200 at $20.83; 200 at $20.84; 200 at $20.91; 300 at $20.92; 600 at
 $20.93; 700 at $20.94; 200 at $20.95; 200 at $20.96; 191 at $20.97; 300 at $20.98; 200 at $20.99; 200 at $21.00; 501 at
 $21.01; 100 at $21.02; 200 at $21.05; 100 at $21.06; 100 at $21.07; 500 at $21.08; 200 at $21.09; and 200 at $21.10</footnote>
        <footnote id="F2">This footnote sets forth additional detail with respect to the transactions described in Footnote 1, as follows:  200 shares
 at $21.15; 100 at $21.18; 100 at $21.20; 100 at $21.21; 100 at $21.23; 100 at $21.27; 100 at $21.28; 300 at $21.34; 100 at
 $21.35; 200 at $21.36; 100 at $21.48; 100 at $21.52; 200 at $21.67; 100 at $21.69; 200 at $21.70; 100 at $21.71; 100 at
 $21.73; 100 at $21.74; 100 at $21.77; 400 at $21.78; 200 at $21.79; 300 at $21.80; 40 at $21.81; 100 at $21.85; 100 at
 $21.87; 100 at $21.92; 200 at $21.93; 100 at $21.94; 200 at $21.96; 200 at $21.99; 200 at $22.00; 100 at $22.02; 500 at
 $22.03; 100 at $22.05; 100 at $22.08; 200 at $22.15; 200 at $22.18; 100 at $22.19; 200 at $22.22; 100 at $22.25; 100 at
 $22.26; 400 at $22.30; 100 at $22.32; 100 at $22.36; 100 at $22.40; 200 at $22.41; 100 at $22.42; 100 at $22.43; 300 at
 $22.44; 100 at $22.45; 200 at $22.48; 200 at $22.49; and 200 at $22.51.</footnote>
        <footnote id="F3">This footnote sets forth additional detail with respect to the transactions described in Footnote 1, as follows:  200 shares
 at $22.52; 400 at $22.53; 200 at $22.54; 200 at $22.56; 200 at $22.57; 800 at $22.58; 500 at $22.59; 400 at $22.60; 100 at
 $22.61; 100 at $22.62; 300 at $22.65; 100 at $22.66; 100 at $22.67; 300 at $22.69; 300 at $22.70; 200 at $22.71; 200 at
 $22.72; 400 at $22.73; 300 at $22.75; 100 at $22.78; 200 at $22.79; 100 at $22.84; 300 at $22.85; 200 at $22.86; 200 at
 $22.90; 100 at $22.92; 200 at $23.00; 200 at $23.03; 100 at $23.14; 200 at $23.26; 100 at $23.29; 200 at $23.38; 100 at
 $23.43; 200 at $23.48; and 200 at $23.57.  The weighted average sales price for these transactions was $21.8127 per share.</footnote>
        <footnote id="F4">The sales were effected in multiple transactions, at varying prices, on July 28, 2006, as follows and as described in
 Footnote 5 below: 143 shares at $20.84; 29 at $20.85; 28 at $20.86; 100 at $20.96; 96 at $20.97; 100 at $20.98; 200 at
 $20.99; 609 at $21.00; 200 at $21.01; 300 at $21.02; 500 at $21.05; 900 at $21.06; 400 at $21.07; 300 at $21.08; 1,400 at
 $21.09; 1,800 at $21.10; 1,800 at $21.11; 1,700 at $21.12; 2,000 at $21.13; 800 at $21.14; 300 at $21.15; 300 at $21.16; 700
 at $21.17; 1,100 at $21.18; 500 at $21.19; 1,900 at $21.20; 300 at $21.21; 200 at $21.22; 400 at $21.23; 600 at $21.24; 100
 at $21.25; 100 at $21.28; 200 at $21.29; and 600 at $21.30.</footnote>
        <footnote id="F5">This footnote sets forth additional detail with respect to the transactions described in Footnote 4, as follows:  100 shares
 at $21.31; 95 at $21.32; 100 at $21.33; 300 at $21.34; 200 at $21.37; 200 at $21.38; 100 at $21.40; 100 at $21.42; 200 at
 $21.45; 100 at $21.52; 100 at $21.90; 600 at $21.91; 300 at $21.92; 200 at $21.93; 200 at $21.94; 200 at $21.95; 400 at
 $21.99; 300 at $22.00; 200 at $22.02; 200 at $22.06; and 100 at $22.07. The weighted average sales price for these
 transactions was $21.2385 per share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Timothy G. Westman,  Assistant Secretary</signatureName>
        <signatureDate>2006-07-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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