<SUBMISSION>
<ACCESSION-NUMBER>0000950123-11-056127
<TYPE>POS AM
<PUBLIC-DOCUMENT-COUNT>1
<FILING-DATE>20110602
<DATE-OF-FILING-DATE-CHANGE>20110602
<FILER>
<COMPANY-DATA>
<CONFORMED-NAME>CLEAN DIESEL TECHNOLOGIES INC
<CIK>0000949428
<ASSIGNED-SIC>3564
<IRS-NUMBER>061393453
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>POS AM
<ACT>33
<FILE-NUMBER>333-171431
<FILM-NUMBER>11889407
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>4567 TELEPHONE ROAD
<STREET2>SUITE 206
<CITY>VENTURA
<STATE>CA
<ZIP>93003
<PHONE>805 639 9458
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>4567 TELEPHONE ROAD
<STREET2>SUITE 206
<CITY>VENTURA
<STATE>CA
<ZIP>93003
</MAIL-ADDRESS>
</FILER>
<DOCUMENT>
<TYPE>POS AM
<SEQUENCE>1
<FILENAME>v59649a1posam.htm
<DESCRIPTION>POS AM
<TEXT>
<HTML>
<HEAD>
<TITLE>posam</TITLE>
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<DIV style="font-family: 'Times New Roman',Times,serif">

<DIV align="center" style="font-size: 10pt; margin-top: 6pt"><B>As filed with the Securities and Exchange Commission on June&nbsp;2, 2011</B>
</DIV>


<DIV align="right" style="font-size: 10pt; margin-top: 0pt"><B>Registration No.&nbsp;333-171431</B>
</DIV>


<DIV style="width: 100%; border-bottom: 2pt solid black; font-size: 1pt">&nbsp;</DIV>
<DIV style="width: 100%; border-bottom: 1pt solid black; font-size: 1pt">&nbsp;</DIV>




<DIV align="center" style="font-size: 14pt; margin-top: 6pt"><B>UNITED STATES<BR>
SECURITIES AND EXCHANGE COMMISSION</B>
</DIV>

<DIV align="center" style="font-size: 12pt"><B>Washington, D.C. 20549</B>
</DIV>

<DIV align="center"><DIV style="FONT-size: 3pt; margin-top: 6pt; width: 26%; border-top: 1px solid #000000">&nbsp;</DIV></DIV>


<DIV align="center" style="font-size: 12pt; margin-top: 6pt"><B>Post-Effective Amendment No.&nbsp;1 to</B>
</DIV>

<DIV align="center" style="font-size: 18pt; margin-top: 0pt"><B>FORM S-1</B>
</DIV>


<DIV align="center" style="font-size: 12pt; margin-top: 0pt"><B>REGISTRATION STATEMENT UNDER<BR>
THE SECURITIES ACT OF 1933</B>
</DIV>

<DIV align="center"><DIV style="FONT-size: 3pt; margin-top: 6pt; width: 26%; border-top: 1px solid #000000">&nbsp;</DIV></DIV>

<DIV align="center" style="font-size: 24pt; margin-top: 6pt"><B>Clean Diesel Technologies, Inc.</B>
</DIV>

<DIV align="center" style="font-size: 8pt">(Exact name of registrant as specified in its charter)</DIV>


<DIV align="center">
<TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
<!-- Begin Table Head -->
<TR style="font-size: 4pt" valign="bottom">
    <TD width="31%">&nbsp;</TD>
    <TD width="3%">&nbsp;</TD>
    <TD width="31%">&nbsp;</TD>
    <TD width="3%">&nbsp;</TD>
    <TD width="31%">&nbsp;</TD>
</TR>
<TR></TR>
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<TR valign="bottom">
    <TD align="center" valign="top"><B>Delaware</B>
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top"><B>2810</B>
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top"><B>06-1393453</B></TD>
</TR>
<TR style="font-size: 8pt" valign="bottom">
    <TD align="center" valign="top"><B>(State or
other jurisdiction
of incorporation or
organization)</B>
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top"><B>(Primary Standard Industrial Classification
Code Number)</B>
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top"><B>(I.R.S. Employer Identification No.)</B></TD>
</TR>
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</TABLE>
</DIV>

<DIV align="center" style="font-size: 10pt; margin-top: 6pt"><B>4567 Telephone Road, Suite&nbsp;206<BR>
Ventura, California 93003<BR>
(805)&nbsp;639-9458</B></DIV>

<DIV align="center" style="font-size: 8pt"><B>(Address, including zip code, and telephone number, including area code, of registrant&#146;s principal executive offices)</B></DIV>


<DIV align="center"><DIV style="FONT-size: 3pt; margin-top: 6pt; width: 26%; border-top: 1px solid #000000">&nbsp;</DIV></DIV>

<DIV align="center" style="font-size: 10pt; margin-top: 6pt"><B>Nikhil A. Mehta<BR>
Chief Financial Officer and Treasurer<BR>
4567 Telephone Road, Suite&nbsp;206<BR>
Ventura, California 93003<BR>
(805)&nbsp;639-9458</B></DIV>

<DIV align="center" style="font-size: 8pt"><B>(Name, address, including zip code, and telephone number, including area code, of agent for service)</B></DIV>


<DIV align="center" style="font-size: 10pt; margin-top: 6pt"><I>Copies to:</I></DIV>

<DIV align="center" style="font-size: 10pt; margin-top: 6pt"><B>Robert M. Smith<BR>
Reed Smith LLP<BR>
101 Second Street, Suite&nbsp;1800<BR>
San Francisco, California 94105<BR>
(415)&nbsp;659-5955</B></DIV>


<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Approximate date of commencement of proposed sale to the public: </B>Not applicable.
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If any of the securities being registered on this Form are to be offered on a delayed or
continuous basis pursuant to Rule&nbsp;415 under the Securities Act of 1933 check the following box.
<FONT style="font-family: Wingdings">&#168;</FONT>
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If this Form is filed to register additional securities for an offering pursuant to Rule
462(b) under the Securities Act, please check the following box and list the Securities Act
registration statement number of the earlier effective registration statement for the same
offering. <FONT style="font-family: Wingdings">&#168;</FONT>
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities
Act, check the following box and list the Securities Act registration statement number of the
earlier effective registration statement for the same offering. <FONT style="font-family: Wingdings">&#168;</FONT>
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities
Act, check the following box and list the Securities Act registration statement number of the
earlier effective registration statement for the same offering. <FONT style="font-family: Wingdings">&#168;</FONT>
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Indicate by check mark whether the registrant is a large accelerated filer, an accelerated
filer, a non-accelerated filer, or a smaller reporting company. See the definitions of &#147;large
accelerated filer,&#148; &#147;accelerated filer&#148; and &#147;smaller reporting company&#148; in Rule&nbsp;12b-2 of the
Exchange Act. (Check one):
</DIV>
<DIV align="center">
<TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
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<TR style="font-size: 4pt" valign="bottom">
    <TD width="22%">&nbsp;</TD>
    <TD width="3%">&nbsp;</TD>
    <TD width="22%">&nbsp;</TD>
    <TD width="3%">&nbsp;</TD>
    <TD width="22%">&nbsp;</TD>
    <TD width="3%">&nbsp;</TD>
    <TD width="22%">&nbsp;</TD>
</TR>
<!-- End Table Head -->
<!-- Begin Table Body -->
<TR valign="bottom">
    <TD nowrap align="left" valign="top">Large accelerated filer <FONT style="font-family: Wingdings">&#168;</FONT>
</TD>
    <TD>&nbsp;</TD>
    <TD nowrap align="center" valign="top">Accelerated filer <FONT style="font-family: Wingdings">&#168;</FONT>
</TD>
    <TD>&nbsp;</TD>
    <TD nowrap align="center" valign="top">Non-accelerated filer <FONT style="font-family: Wingdings">&#168;</FONT><BR>
(Do not check if a smaller reporting company)
</TD>
    <TD>&nbsp;</TD>
    <TD nowrap align="right" valign="top">Smaller reporting company <FONT style="font-family: Wingdings">&#120;</FONT></TD>
</TR>
<!-- End Table Body -->
</TABLE>
</DIV>


<DIV style="width: 100%; border-bottom: 1pt solid black; margin-top: 10pt; font-size: 1pt">&nbsp;</DIV>
<DIV style="width: 100%; border-bottom: 2pt solid black; font-size: 1pt">&nbsp;</DIV>













<P align="center" style="font-size: 10pt"><!-- Folio -->&nbsp;<!-- /Folio -->
</DIV>

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<H5 align="left" style="page-break-before:always">&nbsp;</H5><P>

<DIV style="font-family: 'Times New Roman',Times,serif">










<DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>DEREGISTRATION OF SECURITIES</B>
</DIV>


<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This Post-Effective Amendment No.&nbsp;1 (this &#147;Post-Effective Amendment&#148;) relates to the
Registration Statement on Form S-1 (Registration No.&nbsp;333-171431) (the &#147;Registration Statement&#148;) of
Clean Diesel Technologies, Inc., a Delaware corporation (the &#147;Company&#148;) originally filed on
December&nbsp;27, 2010, as amended on December&nbsp;30, 2010 and declared effective on December&nbsp;30, 2010.
Pursuant to the Registration Statement, the Company registered for resale 709,602 shares of the
Company&#146;s common stock.
</DIV>

<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The Company filed the Registration Statement pursuant to that certain Registration Rights
Agreement dated October&nbsp;15, 2010. The Company and the holders of a majority of the &#147;Registrable
Securities&#148; (as defined in the Registration Rights Agreement) have waived the obligation that the
Company keep the Registration Statement effective. This Post-Effective Amendment is being filed
solely to deregister all of the shares of common stock previously registered under the Registration
Statement that remain unsold under the Registration Statement and to terminate the effectiveness of
the Registration Statement.
</DIV>






<P align="center" style="font-size: 10pt"><!-- Folio -->&nbsp;<!-- /Folio -->
</DIV>

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<H5 align="left" style="page-break-before:always">&nbsp;</H5><P>

<DIV style="font-family: 'Times New Roman',Times,serif">




<DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>SIGNATURES</B>
</DIV>


<DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has
duly caused this registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Ventura, State of California, on the 2<SUP style="FONT-size: 85%; vertical-align: text-top">nd</SUP> day of June,
2011.
</DIV>

<TABLE width="100%" border="0" cellspacing="0" cellpadding="0" style="font-size: 10pt">
<TR>
    <TD width="48%">&nbsp;</TD>
    <TD width="1%">&nbsp;</TD>
    <TD width="1%">&nbsp;</TD>
    <TD width="35%">&nbsp;</TD>
    <TD width="15%">&nbsp;</TD>
</TR>
<TR>
    <TD valign="top" align="left">&nbsp;</TD>
    <TD colspan="3" align="left">CLEAN DIESEL TECHNOLOGIES, INC.<BR><BR>
&nbsp;</TD>
    <TD>&nbsp;</TD>
</TR><TR>
    <TD align="left">&nbsp;</TD>
    <TD valign="top">By:&nbsp;&nbsp;</TD>
    <TD colspan="2" style="border-bottom: 1px solid #000000" align="left">/s/  <FONT style="FONT-variant: SMALL-CAPS">  Charles F. Call</FONT>
&nbsp;</TD>
    <TD>&nbsp;</TD>
</TR><TR>
    <TD align="left">&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD colspan="2" align="left">Charles F. Call&nbsp;</TD>
    <TD>&nbsp;</TD>
</TR><TR>
    <TD align="left">&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD colspan="2" align="left">Chief Executive Officer<BR>
(Principal Executive Officer)&nbsp;</TD>
    <TD>&nbsp;</TD>
</TR>
<TR>
    <TD colspan="5">&nbsp;</TD>
</TR>
</TABLE>
<DIV align="left" style="font-size: 10pt; margin-top: 6pt">Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement
has been signed below by the following persons in the capacities and on the dates indicated.
</DIV>

<DIV align="center">
<TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
<!-- Begin Table Head -->
<TR valign="bottom">
    <TD width="35%">&nbsp;</TD>
    <TD width="5%">&nbsp;</TD>
    <TD width="35%">&nbsp;</TD>
    <TD width="5%">&nbsp;</TD>
    <TD width="15%">&nbsp;</TD>
</TR>
<TR style="font-size: 10pt" valign="bottom">
    <TD nowrap align="center" style="border-bottom: 1px solid #000000"><B>Signature</B></TD>
    <TD>&nbsp;</TD>
    <TD nowrap align="center" style="border-bottom: 1px solid #000000"><B>Title</B></TD>
    <TD>&nbsp;</TD>
    <TD nowrap align="center" style="border-bottom: 1px solid #000000"><B>Date</B></TD>
</TR>

<!-- End Table Head -->
<!-- Begin Table Body -->
<TR valign="bottom" style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/   <FONT style="FONT-variant: SMALL-CAPS"> Charles F. Call</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Charles F. Call</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Director, Chief Executive Officer<BR>
(Principal Executive Officer)
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR valign="bottom" style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/    <FONT style="FONT-variant: SMALL-CAPS">Nikhil A. Mehta</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Nikhil A. Mehta</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Chief Financial Officer<BR>
(Principal Financial Officer)
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR valign="bottom" style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/    <FONT style="FONT-variant: SMALL-CAPS">David E. Shea</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
David E. Shea</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Controller<BR>
(Principal Accounting Officer)
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/    <FONT style="FONT-variant: SMALL-CAPS">*</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Alexander &#147;Hap&#148; Ellis III</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Chairman of the Board
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/   <FONT style="FONT-variant: SMALL-CAPS">*</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Bernard (&#147;Bud&#148;) H. Cherry</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Director
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/    <FONT style="FONT-variant: SMALL-CAPS">*</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Charles R. Engles, Ph.D.</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Director
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/    <FONT style="FONT-variant: SMALL-CAPS">*</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Derek R. Gray</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Director
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<TR style="padding-top: 1em">
    <TD align="left" nowrap valign="top">/s/ <FONT style="FONT-variant: SMALL-CAPS">*</FONT>
<DIV style="font-size: 1pt; border-bottom: 1px solid #000000">&nbsp;</DIV>
Mungo Park</TD>
    <TD>&nbsp;</TD>
    <TD align="center">
Director
</TD>
    <TD>&nbsp;</TD>
    <TD align="center" valign="top">June 2, 2011</TD>
</TR>
<!-- End Table Body -->
</TABLE>
</DIV>


<DIV style="margin-top: 6pt">
<TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">

<TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
    <TD width="1%" nowrap align="left">*</TD>
    <TD width="1%">&nbsp;</TD>
    <TD>The undersigned does hereby sign this registration statement on behalf of the above
indicated director of Clean Diesel Technologies, Inc. pursuant to a power of attorney executed by
such director.</TD>
</TR>

</TABLE>
</DIV>

<TABLE width="100%" border="0" cellspacing="0" cellpadding="0" style="font-size: 10pt">
<TR>
    <TD width="1%">&nbsp;</TD>
    <TD width="1%">&nbsp;</TD>
    <TD width="34%">&nbsp;</TD>
    <TD width="15%">&nbsp;</TD>
    <TD width="49%">&nbsp;</TD>
</TR>
<TR>
    <TD valign="top">By:&nbsp;&nbsp;</TD>
    <TD colspan="2" style="border-bottom: 1px solid #000000" align="left">/s/ Nikhil A. Mehta
&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD align="left">&nbsp;</TD>
</TR><TR>
    <TD>&nbsp;</TD>
    <TD colspan="2" align="left">Nikhil A. Mehta&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD align="left">&nbsp;</TD>
</TR><TR>
    <TD>&nbsp;</TD>
    <TD colspan="2" align="left">Attorney-in-Fact&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD align="left">&nbsp;</TD>
</TR>
<TR>
    <TD colspan="5">&nbsp;</TD>
</TR>
</TABLE>


<P align="center" style="font-size: 10pt"><!-- Folio -->&nbsp;<!-- /Folio -->
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