AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 16, 2004
                                                   1933 ACT FILE NO. 333-______
                                                   1940 ACT FILE NO. 811 - 03763

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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                             -----------------------

                            REGISTRATION STATEMENT ON
                                    FORM S-6

                            ------------------------

                FOR REGISTRATION UNDER THE SECURITIES ACT OF 1933
                     OF SECURITIES OF UNIT INVESTMENT TRUSTS
                            REGISTERED ON FORM N-8B-2

A.   EXACT NAME OF TRUST: CLAYMORE SECURITIES DEFINED PORTFOLIOS, SERIES 203

B.   NAME OF DEPOSITOR: CLAYMORE SECURITIES, INC.

C.   COMPLETE ADDRESS OF DEPOSITOR'S PRINCIPAL EXECUTIVE OFFICES:

                           Claymore Securities, Inc.
                           2455 Corporate West Drive
                             Lisle, Illinois 60532

D.   NAME AND COMPLETE ADDRESS OF AGENT FOR SERVICE:

  Copies to:

      NICHOLAS DALMASO, ESQ.                   ERIC F. FESS
      Senior Managing Director and
      General Counsel
      Claymore Securities, Inc.             Chapman and Cutler LLP
      2455 Corporate West Drive             111 West Monroe Street
      Lisle, Illinois  60532                Chicago, Illinois 60603
      (630) 505-3736                        (312) 845-3000



     It is proposed that this filing will become effective (check appropriate
     box)

/ /  immediately upon filing pursuant to paragraph (b)

/ /  on   (date) pursuant to paragraph (b)

/ /  60 days after filing pursuant to paragraph (a)

/ /  on (date) pursuant to paragraph (a) of rule 485 or 486

/ /  This post-effective amendment designates a new effective date for a
     previously filed post-effective amendment.


E.   TITLE OF SECURITIES BEING REGISTERED: Units of fractional undivided
     beneficial interest.

F.   APPROXIMATE DATE OF PROPOSED SALE TO PUBLIC: As soon as practicable after
     the effective date of the Registration Statement.

/ /  Check box if it is proposed that this filing will become effective on
     (date) at (time) pursuant to Rule 487.

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The registration hereby amends this Registration Statement on such date or dates
as may be necessary to delay its effective date until the registrant shall file
a further amendment which specifically states that this Registration Statement
shall thereafter become effective in accordance with Section 8(a) of the
Securities Act of 1933 or until the Registration Statement shall become
effective on such date as the Commission, acting pursuant to said Section 8(a)
may determine.



                 PRELIMINARY PROSPECTUS DATED NOVEMBER 16, 2004

                             SUBJECT TO COMPLETION


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[LOGO OMITTED]

Claymore Securities Defined Portfolios, Series 203

Real Estate Income Portfolio, Series 3
Utilities Portfolio, Series 4

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     Final prospectuses for prior Series of the Claymore Securities Defined
Portfolios are hereby incorporated by reference and used as part of a
preliminary prospectus for Claymore Securities Defined Portfolios, Series 203
(the "TRUST"). The final prospectus for the Trust is expected to be
substantially similar to the previous prospectuses. However, specific
information with respect to the Trust, including pricing, the size and
composition of the Trust's portfolio, the number of units of the Trust, dates
and summary information regarding the characteristics of securities to be
deposited in the Trust is not now available and will be different from that
shown since Trust has a unique portfolio. Accordingly, the information contained
herein with regard to the previous Trust should be considered as being included
for informational purposes only.

     The Securities and Exchange Commission has not approved or disapproved
these securities or passed upon the adequacy of this Prospectus. Any
representation to the contrary is a criminal offense.

     The information in this Prospectus is not complete and may be changed. We
may not sell these securities until the registration statement filed with the
Securities and Exchange Commission is effective. This Prospectus is not an offer
to sell the securities and it is not soliciting an offer to buy these securities
in any state where the offer or sale is not permitted.

Incorporated herein by reference are the prospectuses from Claymore Securities
Defined Portfolios, Series 164 (Registration No. 333-110558) dated November 19,
2003 and Claymore Securities Defined Portfolios, Series 175 (Registration No.
333-114235) dated April 14, 2004, which shall be used as a preliminary
prospectus for Claymore Securities Defined Portfolios, Series 203. The final
prospectus for Claymore Securities Defined Portfolios, Series 164, was filed
pursuant to rule 497 under the Securities Act on November 21, 2003. The final
prospectus for Claymore Securities Defined Portfolios, Series 175, was filed
pursuant to rule 497 under the Securities Act on April 15, 2004.



                       CONTENTS OF REGISTRATION STATEMENT

         A. Bonding Arrangements of Depositor:

         The Depositor has obtained the following Securities Dealer Blanket Bond
for its officers, directors and employees:

           INSURER/POLICY NO.                            AMOUNT

     National Union Fire Insurance
   Company of Pittsburgh, Pennsylvania                   $250,000
              959-9000

         This Registration Statement comprises the following papers and
         documents.

                  The Facing Sheet
                  The Prospectus
                  The Signatures
                  Consents of Counsel

         The following exhibits:

1.1      Reference Trust Agreement (to be supplied by amendment).

1.1.1    Standard Terms and Conditions of Trust (Reference is made to Exhibit
         1.1.1 to Amendment No.1 to the Registration Statement on Form S-6 for
         Claymore Securities Defined Portfolios, Series 116 (File No. 333-72828
         filed on December 18, 2001).

2.1      Code of Ethics (Reference is made to Exhibit 2.1 to the Registration
         Statement on Form S-6 for Claymore Securities Deferred Portfolios,
         Series 171 (File No. 333-112575 filed on February 19, 2004).

3.1      Opinion of counsel as to legality of the securities being registered
         including a consent to the use of its name in the Registration
         Statement (to be supplied by amendment).

3.2      Opinion of counsel as to Federal Income tax status of the securities
         being registered including a consent to the use of its name in the
         Registration Statement (to be supplied by amendment).

3.3      Opinion of counsel as to New York Income tax status of the securities
         being registered including a consent to the use of its name in the
         Registration Statement (to be supplied by amendment).

3.4      Opinion of counsel as to the Trustee and the Trust (s) including a
         consent to the use of its name in the Registration Statement (to be
         supplied by amendment).

4.1      Consent of Independent Registered Public Accounting Firm (to be
         supplied by amendment).



                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant,
Claymore Securities Defined Portfolios, Series 203 has duly caused this to the
Registration Statement to be signed on its behalf by the undersigned thereunto
duly authorized, in the City of Lisle, and State of Illinois, on the 16th day of
November, 2004.

                                      CLAYMORE SECURITIES DEFINED PORTFOLIOS,
                                        SERIES 203, Registrant

                                      By:  CLAYMORE SECURITIES, INC., Depositor

                                           By:  /S/ NICHOLAS DALMASO
                                               ----------------------
                                                    Nicholas Dalmaso


     Pursuant to the requirements of the Securities Act of 1933, this amended
Registration Statement has been signed below on November 16, 2004 by the
following persons, who constitute a majority of the Board of Directors of
Claymore Securities, Inc.



     SIGNATURE*                           TITLE**                               DATE
                                                                          
                                                                            )    By:    /S/ NICHOLAS DALMASO
                                                                                        --------------------
                                                                            )                  Nicholas Dalmaso
                                                                            )                  Attorney-in-Fact*
                                                                            )
DAVID HOOTEN*                             Chairman of the Board of          )           November 16, 2004
                                          Directors                         )
                                                                            )

/S/ CHARLES MILLINGTON                    Chief Financial Officer                       November 16, 2004
- ----------------------
    CHARLES MILLINGTON

/S/ NICHOLAS DALMASO                      Executive Vice President,                     November 16, 2004
- --------------------                      Secretary, Treasurer and
    NICHOLAS DALMASO                      Director



*    An executed copy of the related power of attorney was filed as Exhibit 6.0
     to Registration Statement No. 333-98345 on August 22, 2002.

**   The titles of the persons named herein represent their capacity in and
     relationship to Claymore Securities, Inc., the Depositor.



            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

     The consent of Grant Thornton LLP to the use of its report and to the
reference to such firm in the Prospectus included in the Registration Statement
will be filed as Exhibit 4.1 to the Registration Statement.

                        CONSENT OF CHAPMAN AND CUTLER LLP

     The consent of Chapman and Cutler LLP to the use of its name in the
Prospectus included in the Registration Statement will be contained in its
opinions to be filed as Exhibits 3.1 and 3.2 to the Registration Statement.

                      CONSENT OF EMMET, MARVIN & MARTIN LLP

     The consent of Emmet, Marvin & Martin LLP to the use of its name in the
Prospectus included in the Registration Statement will be contained in its
opinions to be filed as Exhibits 3.3 and 3.4 to the Registration Statement.




                                   MEMORANDUM


     Re: Claymore Securities Defined Portfolios, Series 203

     The list of securities comprising the trust of the fund, the evaluation,
record and distribution dates and other changes pertaining specifically to the
new series, such as size and number of units of the trust in the fund and the
statement of financial condition of the new fund will be filed by amendment.

                                    1940 ACT

                             FORMS N-8A AND N-8B-2

         Form N-8A and Form N-8B-2 were filed in respect of Claymore Securities
Defined Portfolios, Series 116 (and subsequent series) (File No. 811-03763).


                                    1933 ACT

                                 THE INDENTURE

     The form of the proposed Standard Terms and Conditions of Trust is expected
to be in all respects consistent with the form of the Standard Terms and
Conditions of Trust dated December 18, 2001 relative to Claymore Securities
Defined Portfolios, Series 116.

                                                    CHAPMAN AND CUTLER LLP

Chicago, Illinois
November 16, 2004