Exhibit 10.18.3

THIRD AMENDMENT TO LOAN AGREEMENT

This Third Amendment to Loan Agreement is made and entered into effective as of
this 20th day of January, 2006 by and between SEI INVESTMENTS COMPANY, a
Pennsylvania corporation (“Borrower”), and U.S. BANK NATIONAL ASSOCIATION, a
national banking association (the “Bank”, and, together with the Borrower, the
“Parties”).

W I T N E S S E T H:

WHEREAS, the Parties entered into a Loan Agreement effective as of July 26, 2001
(the “Loan Agreement”);

WHEREAS, the Agreement was previously amended by the First Amendment to Loan
Agreement, dated as of September 15, 2003 (the “First Amendment”); and

WHEREAS the Agreement was previously amended by the Second Amendment to Loan
Agreement, dated as of January 31, 2004 (the “Second Amendment”); and

WHEREAS, the Parties hereby desire to further amend the Loan Agreement (this
amendment herein sometimes called the “Third Amendment”).

NOW, THEREFORE, the Parties agree as follows:

1. Changes in Credit Facility. Section “2(i)” of the Loan Agreement shall be
amended and restated as follows:

(x) the guaranty by the Borrower of the obligations (not exceeding $82,800,000
in aggregate principal amount) of LSV Employee Group, LLC arising under that
certain $82,800,000 credit agreement to be entered into prior to January 31,
2006 by such Person with LaSalle Bank, N.A. as Administrative Agent and the
Lenders party thereto (as such credit agreement may be from time to time
amended, restated or refinanced so long as the outstanding principal amount
thereof is not increased by such amendment, restatement or refinancing) and
obligations arising under interest rate hedging agreements in respect of a
notional amount not exceeding $41,400,000 entered into by LSV Employee Group,
LLC as required by such credit.

2. Effectiveness. This Third Amendment shall be effective upon delivery to Bank
of an original of this Third Amendment, duly executed by Borrower, along with
(unless waived by the Bank) certified resolutions of Borrower’s Board of
Directors authorizing this Third Amendment.

3. Representations, Warranties and Covenants. The Borrower further represents
and warrants that:

(A) This Third Amendment has been duly executed and delivered by Borrower, is
authorized by all requisite corporate action of Borrower and is the legal,
valid, binding and enforceable obligation of Borrower;

(B) The execution and delivery by the Borrower of this Third Amendment will not
constitute a violation of any applicable law or a breach of any provision
contained in Borrower’s Articles or Certificate of Incorporation or By-Laws, or
contained in any order of any court or any other governmental agency or in any
agreement, instrument or document to which Borrower is a party or by which
Borrower or any of its assets or properties are bound;

(C) Except as previously waived by the Bank in writing, there is outstanding no
Event of Default or event which with the giving of notice and/or the passage of
time, would constitute an Event of Default under the Loan Agreement, as of the
effective date of and after giving effect to this Third Amendment; and

(D) All representations, warranties and covenants as to the Borrower set forth
in the Loan Agreement, as amended, or any of the other Loan Documents, as
applicable, shall be deemed restated in all material respects as of the date
hereof.

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4. Miscellaneous.

(A) As amended hereby and by the First and Second Amendments, the Loan Agreement
shall remain in full force and effect, and all references in the Loan Agreement,
as amended (or other Loan Documents issued pursuant to the Loan Agreement, as
amended), shall mean such Loan Agreement as amended hereby and by the First and
Second Amendments.

(B) Capitalized terms used but not defined herein shall have the same meanings
herein as in the Loan Agreement, as amended.

(C) The Borrower shall reimburse Bank for all reasonable out-of-pocket costs and
expenses, including, without limitation, reasonable attorneys’ fees, incurred by
Bank or for which the Bank becomes obligated in connection with or arising out
of this Third Amendment.

(D) Except as amended hereby and by the First and Second Amendments, the Loan
Agreement, as amended, shall be deemed confirmed and on-going in accord with its
terms. Nothing herein, however, shall be deemed an acceptance or waiver as to
proposed future changes in Borrower’s business and structure that, without the
Bank’s consent and/or an additional amendment of the Loan Agreement, might
otherwise be an Event of Default hereunder.

(E) This Third Amendment may be executed in counterparts, all of which
constitute one instrument hereunder.

IN WITNESS WHEREOF, the parties have executed this Third Amendment as of the
date noted above.

 

U.S. BANK N.A.   SEI INVESTMENTS COMPANY By:  

/s/ Patrick McGraw

  By:  

/s/ Kathy Heilig

  Patrick McGraw     Kathy Heilig   Vice President     Controller