As filed with the Securities and Exchange Commission on July 3, 2012
================================================================================
                                           1933 Act Registration No. 333-171759
                                            1940 Act Registration No. 811-22519


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

                                   FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933                     [ ]
Pre-Effective Amendment No. __                                              [ ]
Post-Effective Amendment No. 15                                             [X]
                                     and/or
REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940             [ ]
Amendment No. 16                                                            [X]


                  FIRST TRUST EXCHANGE-TRADED ALPHADEX FUND II
               (Exact name of registrant as specified in charter)

                       120 East Liberty Drive, Suite 400
                            Wheaton, Illinois 60187
              (Address of Principal Executive Offices) (Zip Code)


       REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (800) 621-1675

                       W. Scott Jardine, Esq., Secretary
                  First Trust Exchange-Traded AlphaDEX Fund II
                           First Trust Advisors L.P.
                       120 East Liberty Drive, Suite 400
                            Wheaton, Illinois 60187
                    (Name and Address of Agent for Service)

                                    Copy to:
                               Eric F. Fess, Esq.
                             Chapman and Cutler LLP
                             111 West Monroe Street
                            Chicago, Illinois 60603


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

[ ] immediately upon filing pursuant to paragraph (b)
[X] on August 2, 2012 pursuant to paragraph (b)
[ ] 60 days after filing pursuant to paragraph (a)(1)
[ ] on (date) pursuant to paragraph (a)(1)
[ ] 75 days after filing pursuant to paragraph (a)(2)
[ ] on (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

[X] this post-effective amendment designates a new effective date for a
    previously filed post-effective amendment.





                  CONTENTS OF POST-EFFECTIVE AMENDMENT NO. 15

      This Post-Effective Amendment to the Registration Statement comprises the
following papers and contents:


      The Facing Sheet

      The sole purpose of this filing is to delay the effectiveness of the
Registrant's Post-Effective Amendment No. 9, as it relates to First Trust Global
Agriculture AlphaDEX(R) Fund, a series of the Registrant, until August 2, 2012.
Parts A, B and C of the Registrant's Post-Effective Amendment No. 9 under the
Securities Act of 1933 as it relates to First Trust Global Agriculture
AlphaDEX(R) Fund, a series of the Registrant, filed on April 20, 2012, are
incorporated by reference herein.

      Signatures




                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933 and the
Investment Company Act of 1940, the Registrant certifies that it meets all of
the requirements for effectiveness of this Registration Statement under rule
485(b) under the Securities Act and has duly caused this Registration Statement
to be signed on its behalf by the undersigned, duly authorized, in the City of
Wheaton, and State of Illinois, on the 3rd day of July, 2012.

                                   FIRST TRUST EXCHANGE-TRADED ALPHADEX FUND II



                                   By: /s/ Mark R. Bradley
                                      -----------------------------------------
                                      Mark R. Bradley, President and Chief
                                      Executive Officer


      Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the date indicated:




SIGNATURE                               TITLE                                 DATE
                                                                        
                                        President and Chief Executive         July 3, 2012
/s/ Mark R. Bradley                     Officer
-------------------------------------
    Mark R. Bradley

                                        Treasurer, Chief Financial Officer    July 3, 2012
/s/ James M. Dykas                      and Chief Accounting Officer
-------------------------------------
    James M. Dykas

                                                         )
James A. Bowen*                                  Trustee )
                                                         )
                                                         )
Richard E. Erickson*                             Trustee )
                                                         )
                                                         )
Thomas R. Kadlec*                                Trustee )                    BY: /s/ W. Scott Jardine
                                                         )                       -------------------------------
                                                         )                            W. Scott Jardine
Robert F. Keith*                                 Trustee )                            Attorney-In-Fact
                                                         )                            July 3, 2012
                                                         )
Niel B. Nielson*                                 Trustee )
                                                         )



*  Original powers of attorney authorizing James A. Bowen, W. Scott Jardine and
   Eric F. Fess, to execute Registrant's Registration Statement, and Amendments
   thereto, for each of the trustees of the Registrant on whose behalf this
   Registration Statement is filed, were previously executed, filed as an
   exhibit and are incorporated by reference herein.