S-1MEF

As filed with the Securities and Exchange Commission on June 28, 2011

Registration No. 333-      

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Form S-1

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

Clean Diesel Technologies, Inc.
(Exact name of registrant as specified in its charter)

Delaware
(State or other jurisdiction of
incorporation or organization) 2810
(Primary Standard Industrial
Classification Code Number) 06-1393453
(I.R.S. Employer
Identification No.)

4567 Telephone Road, Suite 206
Ventura, California 93003
(805) 639-9458
(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Nikhil A. Mehta
Chief Financial Officer and Treasurer
4567 Telephone Road, Suite 206
Ventura, California 93003
(805) 639-9458
(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Robert M. Smith
Marianne C. Sarrazin
Reed Smith LLP
101 Second Street, Suite 1800
San Francisco, California 94105
(415) 659-5955 R. Scott Shean
B. Shayne Kennedy
Latham & Watkins LLP
650 Town Center Drive, 20^th Floor
Costa Mesa, California 92626-1925
(714) 540-1235

Approximate date of commencement of proposed sale to the public:  As soon as practicable after the effective date of this Registration Statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box.  o

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.  þ  333-174680

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.  o

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.  o

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 “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer o Accelerated filer o Non-accelerated filer o
(Do not check if a smaller reporting company) Smaller reporting company þ

CALCULATION OF REGISTRATION FEE

		Proposed Maximum	Proposed Maximum	Amount of
Title of Each Class of	Amount	Offering	Aggregate	Registration
Securities to be Registered	to be Registered(1)	Price per Share(2)	Offering Price(3)	Fee
Common stock, par value $0.01 per share	718,750	$3.75	$2,695,312	$312.92

(1)	The shares being registered under this Registration Statement are in addition to the 2,415,000 shares registered pursuant to the Registration Statement on Form S-1 (333-174680).
(2)	Based on the public offering price of $3.75 per share.
(3)	Estimated in accordance with Rule 457(a) of the Securities Act of 1933.

This Registration Statement shall become effective upon filing with the Securities and Exchange Commission in accordance with Rule 462(b) under the Securities Act of 1933, as amended.

EXPLANATORY NOTE AND INCORPORATION BY REFERENCE

This registration statement is being filed with respect to the registration of additional shares of common stock, par value $0.01 per share, of Clean Diesel Technologies, Inc., a Delaware corporation, pursuant to Rule 462(b) under the Securities Act of 1933, as amended. The contents of the earlier registration statement on Form S-1, as amended (File No. 333-174680), which was declared effective by the Securities and Exchange Commission on June 28, 2011, and all exhibits thereto are incorporated in this registration statement by reference.

The required opinion and consents are listed on an Exhibit Index attached hereto and filed herewith.

The Registrant hereby certifies that it (i) has initiated and released a wire transfer to transmit the filing fee set forth on the cover page of this Registration Statement to the Securities and Exchange Commission’s account as soon as practicable (but no later than the close of business on June 29, 2011), (ii) will not revoke such wire transfer, and (iii) has sufficient funds in the relevant account to cover the amount of such filing fee.

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 16.   Exhibits and Financial Statement Schedules.

All exhibits filed with or incorporated by reference in Registration Statement No. 333-174680 are incorporated by reference into, and shall be deemed part of, this registration statement, except the following, which are filed herewith.

Exhibit No.			Description of Exhibit
	5	.1*	Opinion of Reed Smith LLP as to validity of the securities issued.
	23	.1*	Consent of KPMG LLP, Independent Registered Public Accounting Firm.
	23	.2	Consent of Reed Smith LLP (included in Exhibit 5.1).
	24	.1†	Powers of Attorney

*	Filed or furnished herewith
†	Included on the signature page to the Registrant’s Registration Statement on Form S-1 (File No. 333-174680) filed with the Commission on June 2, 2011

II-1

SIGNATURES

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 28th day of June, 2011.

CLEAN DIESEL TECHNOLOGIES, INC.

By:  /s/  Charles F. Call

Charles F. Call

Chief Executive Officer

(Principal Executive Officer)

Signature		Title	Date
/s/  Charles F. Call Charles F. Call		Director, Chief Executive Officer (Principal Executive Officer)	June 28, 2011
/s/  Nikhil A. Mehta Nikhil A. Mehta		Chief Financial Officer (Principal Financial Officer)	June 28, 2011
/s/  * David E. Shea		Controller (Principal Accounting Officer)	June 28, 2011
/s/  * Alexander “Hap” Ellis III		Chairman of the Board	June 28, 2011
/s/  * Bernard (“Bud”) H. Cherry		Director	June 28, 2011
/s/  * Charles R. Engles, Ph.D.		Director	June 28, 2011
/s/  * Mungo Park		Director	June 28, 2011
By:	/s/  Nikhil A. Mehta Nikhil A. Mehta, Attorney-in-Fact

* The undersigned does hereby sign this registration statement on behalf of the above indicated director and executive officer of Clean Diesel Technologies, Inc. pursuant to a power of attorney executed by such director and such executive officer.

II-2

EX-5.1

Exhibit 5.1

Reed Smith LLP
101 Second Street
Suite 1800
San Francisco, CA 94105-3659
+1 415 543 8700
Fax +1 415 391 8269
reedsmith.com

June 28, 2011

Clean Diesel Technologies, Inc.
4567 Telephone Road, Suite 206
Ventura, CA 93003

Ladies and Gentlemen:

     We have acted as counsel to Clean Diesel Technologies, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing on June 29, 2011 with the Securities and Exchange Commission (the “Commission”) pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “Securities Act”) of the Registration Statement on Form S-1 (the “Abbreviated Registration Statement”) for the registration of an aggregate of 718,750 shares (the “Additional Shares”) of the Company’s common stock, $0.01 par value per share (the “Common Stock”). The Additional Shares are being offered for sale together with the 2,415,000 shares of Common Stock (the “Initial Shares”) previously registered pursuant to the Registration statement on Form S-1 (333-174680) of the Company that was declared effective by the Commission on June 28, 2011 (the “Initial Registration Statement”). Of the Initial Shares and Additional Shares (collectively, the “Shares”) (i) up to 3,053,750 Shares will be issued and sold by the Company, including up to 408,750 Shares issuable upon exercise of an over-allotment option granted by the Company (the “Company Shares”) and (ii) 80,000 Shares (the “Selling Stockholder Shares”) will be sold by certain stockholders of the Company (the “Selling Stockholders”). The Shares are to be sold by the Company and the Selling Stockholders pursuant to an underwriting agreement (the “Underwriting Agreement”) to be entered into by and among the Company, the Selling Stockholders and Roth Capital Partners, LLC, as Representative of the several underwriters named therein, the form of which has been filed as Exhibit 1.1 to the Initial Registration Statement.

     In rendering the opinion set forth herein, we have examined originals or copies, certified or otherwise identified to our satisfaction, of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary or advisable.

Clean Diesel Technologies, Inc.
June 29, 2011
Page 2

     In such examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all items submitted to us as originals, the conformity with originals of all items submitted to us as copies, and the authenticity of the originals of such copies. As to any facts material to the opinions expressed herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Company and public officials. Our opinion in clause (ii) below, insofar as it relates to the Selling Stockholder Shares being fully paid, is based solely on a certificate of the Chief Financial Officer of the Company confirming the Company’s receipt of the consideration called for by the applicable resolutions authorizing the issuance of such Selling Stockholder Shares.

     This opinion is based solely on the General Corporation Law of the State of Delaware (including all related provisions of the Delaware Constitution and all reported judicial decisions interpreting the General Corporation Law of the State of Delaware and the Delaware Constitution).

     Based upon and subject to the foregoing, we are of the opinion that (i) the Company Shares have been duly authorized for issuance and, when issued, delivered and paid for in accordance with the terms of the Underwriting Agreement, the Company Shares will be validly issued, fully paid and nonassessable, and (ii) the Selling Stockholder Shares have been duly authorized and are validly issued, fully paid and nonassessable.

     We consent to the inclusion of this opinion as an exhibit to the Abbreviated Registration Statement and further consent to all references to us under the caption “Legal Matters” in the Prospectus forming party of the Initial Registration Statement. In giving this consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

Very truly yours,

/s/ Reed Smith LLP

Reed Smith LLP

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EX-23.1

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

The Board of Directors
Clean Diesel Technologies, Inc.:

We consent to the use of our report dated March 31, 2011, with respect to the consolidated balance sheets of Clean Diesel Technologies, Inc. (the Company) as of December 31, 2010 and 2009, and the related consolidated statements of operations, stockholders’ equity and comprehensive loss, and cash flows for the years then ended, incorporated herein by reference.

Our report dated March 31, 2011 contains an explanatory paragraph that states that the Company has suffered recurring losses from operations and has an accumulated deficit that raise substantial doubt about its ability to continue as a going concern. The consolidated financial statements do not include any adjustments that might result from the outcome of that uncertainty.

/s/ KPMG LLP
Los Angeles, California
June 28, 2011