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AOC13G1.doc
SECURITIES AND EXCHANGE COMMISSION
 Washington, D.C. 20549
SCHEDULE 13G
Under the Securities Exchange Act of 1934
(Amendment No. 1)*
Aon Corporation
 (Name of Issuer)

Common Stock
 (Title of Class and Securities)

037389103
(CUSIP Number of Class of Securities)
Check the appropriate box to designate the rule pursuant to which
this
Schedule is filed:
/X/ Rule 13d-1(b)
/ / Rule 13d-1(c)
/ / Rule 13d-1(d)
* The remainder of this cover page shall be filled out for a
reporting person's initial filing on this form with respect to the
subject class of securities, and for any subsequent amendment
containing information which would alter the disclosures provided
in a prior page.
The information required in the remainder of this cover page shall
not be deemed to be "filed" for the purpose of Section 18 of the
Securities Exchange Act of 1934 ("Act") or otherwise subject to
the
liabilities of that section of the Act but shall be subject to all
other provisions of the Act (however, see the Notes).
(Continued on following page(s))

CUSIP No. 037389103
13G
__________________________________________________________________
___________
(1)  NAMES OF REPORTING PERSONS
     Southeastern Asset Management, Inc.      I.D. No. 62-0951781
__________________________________________________________________
___________
(2)  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:
                                              (a)
                                              (b) X
__________________________________________________________________
___________
(3)  SEC USE ONLY
__________________________________________________________________
___________
(4)  CITIZENSHIP OR PLACE OF ORGANIZATION
     Tennessee
__________________________________________________________________
___________
                                   :(5) SOLE VOTING POWER
                                   :   (Discretionary Accounts)
NUMBER OF SHARES BENEFICIALLY      :      17,112,000 shares
OWNED BY EACH REPORTING PERSON
__________________________________________
WITH                               :(6) SHARED OR NO VOTING POWER

                                         12,057,000 shares
(shared)
                                          4,063,800 shares (No
Vote)

__________________________________________
                                   :(7) SOLE DISPOSITIVE POWER
                                        (Discretionary Accounts)
                                   :      21,138,800  shares

__________________________________________
                                   :(8)  SHARED DISPOSITIVE POWER

                                   :      12,057,000 shares
(Shared)
                                              37,000 shares (None)
__________________________________________________________________
___________
(9)  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
      33,232,800 shares
__________________________________________________________________
___________
(10)  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES
      CERTAIN SHARES -X- See Items 4(c)(iii) and 4(c)(iv).
__________________________________________________________________
___________
(11)  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
       10.7 %
__________________________________________________________________
___________
(12)  TYPE OF REPORTING PERSON
      IA
__________________________________________________________________
___________

CUSIP No.  037389103                                     13G
__________________________________________________________________
___________
(1)  NAMES OF REPORTING PERSONS
     O. Mason Hawkins                         I.D. No. 257-72-3256
__________________________________________________________________
___________
(2)  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:
                                              (a)
                                              (b) X
__________________________________________________________________
___________
(3)  SEC USE ONLY
__________________________________________________________________
___________
(4)  CITIZENSHIP OR PLACE OF ORGANIZATION
     Citizen of United States
__________________________________________________________________
___________
                                   :(5) SOLE VOTING POWER
                                   :   (Discretionary Accounts)
NUMBER OF SHARES BENEFICIALLY      :    None
OWNED BY EACH REPORTING PERSON
__________________________________________
WITH                               :(6) SHARED VOTING POWER

                                   :    None

__________________________________________
                                   :(7) SOLE DISPOSITIVE POWER

                                   :    None

__________________________________________
                                   :(8) SHARED DISPOSITIVE POWER

                                   :    None
__________________________________________________________________
___________
(9)  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

       None  (See Item 3 )
__________________________________________________________________
___________
(10)  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES
      CERTAIN SHARES
__________________________________________________________________
___________
(11)  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
      0.0%
__________________________________________________________________
___________
(12)  TYPE OF REPORTING PERSON
      IN
__________________________________________________________________
___________

Item 1.

     (a). Name of Issuer: Aon Corporation

     (b). Address of Issuer's Principal Executive Offices:

          200 E. Randolph Street
         Chicago, Illinois 60601

Item 2.

     (a) and (b). Names and Principal Business Addresses of
Persons
         Filing:

     (1)       Southeastern Asset Management, Inc.
               6410 Poplar Ave., Suite 900
               Memphis, TN 38119

     (2)       Mr. O. Mason Hawkins
               Chairman of the Board and C.E.O.
               Southeastern Asset Management, Inc.
               6410 Poplar Ave., Suite 900
               Memphis, TN 38119

     (c). Citizenship:

          Southeastern Asset Management, Inc. - A Tennessee
     corporation

          Mr. O. Mason Hawkins - U.S. Citizen

     (d). Title of Class of Securities:  Common stock (the
            "Securities").

     (e). Cusip Number:  037389103

Item 3.  If this statement is filed pursuant to Rules 13d-1 (b) or
 13d-2 (b), check whether the person filing is a:

(e)   Investment Adviser registered under Section 203 of the
     Investment Advisers Act of 1940.  This statement is being
filed
     by Southeastern Asset Management, Inc. as a registered
investment
     adviser. All of the securities covered by this report are
owned
     legally by Southeastern's investment advisory clients and
none
     are owned directly or indirectly by Southeastern.  As
permitted
     by Rule 13d-4, the filing of this statement shall not be
construed
     as an admission that Southeastern Asset Management, Inc. is
the
     beneficial owner of any of the securities covered by this
statement.

(g)  Parent Holding Company.  This statement is also being filed
  by
     Mr. O. Mason Hawkins, Chairman of the Board and C.E.O. of
     Southeastern Asset Management, Inc. in the event he could be
     deemed to be a controlling person of that firm as the result
of
     his official positions with or ownership of its voting
securities.
     The existence of such control is expressly disclaimed.  Mr.
Hawkins
     does not own directly or indirectly any securities covered by
     this statement for his own account.  As permitted by Rule 13d-
4,
     the filing of this statement shall not be construed as an
admission
     that Mr. Hawkins is the beneficial owner of any of the
securities
     covered by this statement.
Item 4. Ownership:

     (a). Amount Beneficially Owned: (At 4/30/03)
            33,232,800 shares

     (b). Percent of Class:
            10.7 %

          Above percentage is based on 311,518,091 shares of
common stock outstanding.

     (c). Number of shares as to which such person has:

          (i).   sole power to vote or to direct the vote:

                    17,112,000 shares

          (ii).  shared or no power to vote or to direct the vote:

                 Shared - 12,057,000 shares.
                 Securities owned by the following series of
Longleaf
                 Partners Funds Trust, an open-end management
                 investment company registered under the
Investment
                 Company Act of 1940, as follows:

                    Longleaf Partners Fund - 12,057,000

              No Power to Vote - 4,063,800 shares.  This figure
         does not            include 655,000 shares held by
         completely non-discretionary
         accounts over which the filing parties have neither
         voting nor               dispositive power and for which
         the filing parties disclaim             beneficial
         ownership.

          (iii). sole power to dispose or to direct the
disposition
                 of:

                    21,138,800 shares

          (iv).  shared or no power to dispose or to direct the
                 disposition of:

                 Shared - 12,057,000 shares
                 Securities owned by the following series of
Longleaf
                 Partners Funds Trust, an open-end management
                 investment company registered under the
Investment
                 Company Act of 1940, as follows:

                    Longleaf Partners Fund - 12,057,000

              No Power - 37,000 shares.  This figure does not
         include 655,000 shares held by completely non-
         discretionary                           accounts over
         which the filing parties have neither voting nor
         dispositive power and for which the filing parties
         disclaim            beneficial ownership.

Item 5. Ownership of Five Percent or Less of a Class:  N/A

Item 6. Ownership of More Than Five Percent on Behalf of Another
        Person:  N/A

Item 7. Identification and Classification of the Subsidiary Which
        Acquired the Security Being Reported on By the Parent
        Holding Company:  N/A

Item 8. Identification and Classification of Members of the Group:
        N/A

Item 9. Notice of Dissolution of Group:  N/A

Item 10. Certification:

By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired in the
ordinary course of business and were not acquired for the purpose
and do not have the effect of changing or influencing the control
of the issuer of such securities and were not acquired in
connection with or as a participant in any transaction having such
purposes or effect.

                            Signatures

After reasonable inquiry and to the best of the knowledge and
belief of the undersigned, the undersigned certifies that the
information set forth in this statement is true, complete, and
correct.

Dated: May 8, 2003

                              Southeastern Asset Management, Inc.

                              By  /s/ Andrew R. McCarroll
_______________________________________________
                         Andrew R. McCarroll
                              Vice President and General Counsel

                         O. Mason Hawkins, Individually

                                /s/ O. Mason Hawkins

_______________________________________________

                       Joint Filing Agreement

In accordance with Rule 13d-1(f) under the Securities Exchange Act
of 1934, the persons or entities named below agree to the joint
filing on behalf of each of them of this Schedule 13G with respect
to the Securities of the Issuer and further agree that this joint
filing agreement be included as an exhibit to this Schedule 13G.
In
evidence thereof, the undersigned hereby execute this Agreement as
of May 8, 2003.

                         Southeastern Asset Management, Inc.

                              By  /s/ Andrew R. McCarroll
_______________________________________________
                         Andrew R. McCarroll
                              Vice President and General Counsel

                         O. Mason Hawkins, Individually

                                /s/ O. Mason Hawkins

_______________________________________________