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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>0000950103-04-000088.txt : 20040122
<SEC-HEADER>0000950103-04-000088.hdr.sgml : 20040122
<ACCEPTANCE-DATETIME>20040122180444
ACCESSION NUMBER:		0000950103-04-000088
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20040122
FILED AS OF DATE:		20040122

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:		SIX SHATTUCK RD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
		BUSINESS PHONE:		9789752350

	MAIL ADDRESS:	
		STREET 1:		SIX SHATTUCK ROAD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810

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:		04538678

	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>jan2204_form4ex.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<!-- - EDGAR Ease Plus 1.0                                   07/25/03  TT    -->
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
   <periodOfReport>2004-01-22</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>P O BOX 4100</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>2004-01-21</value>
      </transactionDate>
      <transactionCoding>
         <transactionFormType>4</transactionFormType>
         <transactionCode>S</transactionCode>
         <equitySwapInvolved>0</equitySwapInvolved>
      </transactionCoding>
      <transactionAmounts>
         <transactionShares>
           <value>1714286</value>
         </transactionShares>
         <transactionPricePerShare>
           <value>25.0687</value>
         </transactionPricePerShare>
         <transactionAcquiredDisposedCode>
           <value>D</value>
         </transactionAcquiredDisposedCode>
      </transactionAmounts>
      <postTransactionAmounts>
         <sharesOwnedFollowingTransaction>
           <value>1322325</value>
         </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
         <directOrIndirectOwnership>
            <value>D</value>
         </directOrIndirectOwnership>
      </ownershipNature>
   </nonDerivativeTransaction>
   <nonDerivativeHolding>
      <securityTitle>
         <value>Common Stock</value>
      </securityTitle>
      <postTransactionAmounts>
         <sharesOwnedFollowingTransaction>
           <value>8963389</value>
         </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
         <directOrIndirectOwnership>
            <value>I</value>
            <footnoteId id="F1"/>
         </directOrIndirectOwnership>
         <natureOfOwnership>
            <value>through a subsidiary</value>
         </natureOfOwnership>
      </ownershipNature>
   </nonDerivativeHolding>
 </nonDerivativeTable>
   <footnotes>
      <footnote id="F1"> The reported securities are owned directly by Astec America, Inc.  The Reporting Person is the ultimate parent company of Astec  America, Inc.</footnote>
   </footnotes>
   <remarks>Please see attached Joint Filer Information.</remarks>
   <ownerSignature>
      <signatureName>/s/ Harley M. Smith, Assistant Secretary of Emerson Electric Co.</signatureName>
      <signatureDate>2004-01-22</signatureDate>
   </ownerSignature>
   <ownerSignature>
      <signatureName>/s/ Harley M. Smith, Secretary of Astec America, Inc.</signatureName>
      <signatureDate>2004-01-22</signatureDate>
   </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-99.1
<SEQUENCE>3
<FILENAME>jan2204_form4-ex9901.htm
<TEXT>
<html>
<head>
<title></title>
</head>
<body leftmargin="50p" marginwidth="50p">
<p align="right">Exhibit 99.1</p>
<p align="right">&nbsp;</p>
<p align="center">Joint Filer Information </p>
<p align="center">&nbsp; </p>
<blockquote>
  <blockquote>
    <p>Astec America, Inc., 5810 Van Allen Way , Carlsbad, California 92008, has designated Emerson
      Electric Co. as the &#147;Designated Filer&#148; for the purposes of the attached Form 4.</p>
    <p>Issuer &amp; Ticker Symbol: MKS Instruments, Inc. (MKSI)</p>
    <p>Date of Event Requiring Statement: 01/21/04 </p>
  </blockquote>
</blockquote>
<p>&nbsp;</p>
<blockquote>
  <blockquote>
    <p>Signature:<u> /s/ Harley M. Smith&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </u>
      <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;By: Harley M. Smith, Assistant Secretary of<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Emerson Electric Co. </p>
  </blockquote>
</blockquote>
<p>&nbsp;</p>
<blockquote>
  <blockquote>
    <p>Signature:<u> /s/ Harley M. Smith&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </u> <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;By: Harley M. Smith,  Secretary of<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Astec America, Inc.</p>
  </blockquote>
</blockquote>
<p>&nbsp; </p>
</body>
</html>

</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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