Exhibit (i)(3)

                                ROPES & GRAY LLP
                             One International Place
                        Boston, Massachusetts 02110-2624




                                                              June 2, 2005


State Street Institutional Investment Trust
P.O. Box 1713
Boston, MA 02105-1713

Ladies and Gentlemen:

         We have acted as counsel to State Street Institutional Investment Trust
(the "Trust"). In connection with this opinion, we have examined:

         (a)     A copy of the Agreement and Declaration of Trust of the Trust,
                 dated February 16, 2000 (the "Declaration of Trust"), certified
                 by the Assistant Secretary of the Trust;

         (b)     Copies of Amendments No. 1, No. 2, and No. 3 to the Declaration
                 of Trust, certified by the Assistant Secretary of the Trust;

         (c)     A copy of the Third Amended and Restated By-Laws of the Trust
                 certified by the Assistant Secretary of the Trust;

         (d)     A certificate of the Secretary of State of The Commonwealth of
                 Massachusetts dated May 24, 2005 certifying as to the authority
                 of the Trust to exercise in The Commonwealth all of the powers
                 recited in the Declaration of Trust, as amended, and to
                 transact business in The Commonwealth;

         (e)     A certificate of the Assistant Secretary of the Trust dated
                 June 2, 2005 as to, among other things, certain actions of the
                 Trustees of the Trust; and

         (e)     Such other certificates, documents, and records as we have
                 deemed necessary for purposes of this opinion.

         In our examination, we have assumed the genuineness of all signatures,
the legal capacity of all natural persons, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as certified or photostatic copies, and the
authenticity of the originals of such latter documents.




State Street Institutional Investment Trust   -2-                   June 2, 2005

         We have made such examination of Massachusetts law as we have deemed
relevant for purposes of this opinion. We express no opinion as to the effect of
laws, rules, and regulations of any state or jurisdiction other than The
Commonwealth of Massachusetts.

         You have advised us that the Trust intends to offer for sale Class R
shares of beneficial interest of the State Street Equity 500 Index Fund
(collectively, the "Shares").

         For purposes of this opinion, we have assumed that all Shares will be
sold for consideration that will be in each case at least equal to the
applicable net asset value per Share. In addition, we have assumed that any and
all conditions established by resolution of the Trustees to the authorization or
issuance of the Shares will have been satisfied in full prior to, and in respect
of, such issuance.

         We assume that appropriate action has been taken to register or qualify
the sale of the Shares under any applicable state and federal laws regulating
offerings and sales of securities.

         Based upon and subject to the foregoing, we are of the opinion that:

         1.   The Trust is a legally organized and validly existing voluntary
association with transferable shares of beneficial interest under the laws of
The Commonwealth of Massachusetts and is authorized to issue an unlimited number
of Shares.

         2.   Shares issued and sold after the date hereof will be validly
issued, fully paid, and nonassessable by the Trust.

         The Trust is an entity of the type commonly known as a "Massachusetts
business trust". Under Massachusetts law, shareholders could, under certain
circumstances, be held personally liable for the obligations of the Trust.
However, the Declaration of Trust, as amended, disclaims shareholder liability
for obligations of the Trust and requires that notice of such disclaimer be
given in every note, bond, contract, instrument, certificate, or undertaking
made or issued on behalf of the Trust by its Trustees or officers. The
Declaration of Trust, as amended, provides for indemnification out of the
property of the series in question for all loss and expense of any shareholder
of that series held personally liable for the obligations of the series solely
by reason of his being or having been a shareholder of the series. Thus, the
risk of a shareholder's incurring financial loss on account of shareholder
liability should be limited to circumstances in which the series in question
would itself be unable to meet its obligations.

         We consent to the filing of this opinion as an exhibit to the
Registration Statement.

                                         Very truly yours,


                                         /s/ Ropes & Gray LLP