Exhibit 5

                              [PMRW LETTERHEAD]

203 North LaSalle Street
Suite 1800
Chicago, Illinois  60601-1293
www.piperrudnick.com
PHONE  (312) 368-4000
FAX    (312) 236-7516



                                                                  March 2, 2001

ERP Operating Limited Partnership
c/o Board of Trustees
Equity Residential Properties Trust
Two North Riverside Plaza
Suite 400
Chicago, Illinois  60606

Ladies and Gentlemen:

     We have served as counsel for ERP Operating Limited Partnership, an
Illinois limited partnership (the "Operating Partnership"), the general
partner of which is Equity Residential Properties Trust, a Maryland real
estate investment trust (the "Company"), in connection with the Operating
Partnership's registration statement on Form S-3 (the "Registration
Statement") previously declared effective by the Securities and Exchange
Commission relating to unsecured senior debt securities in a maximum
aggregate offering price of $1,000,000,000 (the "Securities") (SEC File No.
333-44594), all of which Securities may be offered and sold by the Operating
Partnership from time to time as set forth in the prospectus filed as part of
the Registration Statement and the registration statement on Form S-3 (No.
333-45557), which prospectus includes $430,000,000 aggregate principal amount
of debt securities from such registration statement (the "Prospectus"), and
as to be set forth in one or more supplements to the Prospectus (each, a
"Prospectus Supplement"). This opinion letter is rendered in connection with
the proposed public offering by the Operating Partnership of $300,000,000
principal amount of its 6.95% Notes due March 2, 2011 (the "Notes") as
described in a Prospectus Supplement dated February 27, 2001. This opinion
letter is furnished to you at your request to enable the Operating
Partnership to continue to fulfill the requirements of Item 601(b)(5) of
Regulation S-K, 17 C.F.R. 229.601(b)(5), in connection with the Registration
Statement.

     We have examined and relied and base our opinion on originals or copies,
certified or otherwise identified to our satisfaction, of the following
documents and records and upon such matters of law as we have deemed necessary
for the purposes of this opinion.

     1.   An executed copy of the Registration Statement and a copy of the
          Prospectus and Prospectus Supplement dated February 27, 2001.



                                               ERP Operating Limited Partnership
                                                                   March 2, 2001
                                                                          Page 2

     2.   The Second Amended and Restated Declaration of Trust of the Company
          (the "Declaration of Trust"), as certified by the Assistant Secretary
          of the Company on the date hereof as then being complete, accurate and
          in effect.

     3.   The Third Amended and Restated Bylaws of the Company, as certified by
          the Assistant Secretary of the Company on the date hereof as then
          being complete, accurate and in effect.

     4.   The Fifth Amended and Restated Agreement of Limited Partnership of the
          Operating Partnership dated as of August 1, 1998, certified by the
          Assistant Secretary of the Company, as the general partner of the
          Operating Partnership, on the date hereof as then being complete,
          accurate and in effect.

     5.   Resolutions of the Board of Trustees of the Company, as the general
          partner of the Operating Partnership, adopted on November 14, 1997,
          January 14, 1998, August 21, 2000 and January 18, 2001 relating to
          the filing of the Registration Statement and related matters, and by
          the Pricing Committee of the Board of Trustees on February 27, 2001,
          relating to the offering of the Notes, each as certified by the
          Assistant Secretary of the Company on the date hereof as then being
          complete, accurate and in effect.

     6.   The Standard Underwriting Provisions dated August 25, 2000, the terms
          of which are incorporated by reference into the related Terms
          Agreement dated February 27, 2001 between the Operating Partnership
          and Merrill Lynch & Co., Merrill Lynch, Pierce, Fenner & Smith
          Incorporated, Chase Securities Inc., Banc of America Securities LLC
          and Salomon Smith Barney Inc. (collectively, the "Underwriting
          Agreement").

     The opinions set forth herein are qualified as stated therein and are
qualified further by the following:

          (a) This opinion is based upon existing laws, ordinances and
     regulations in effect as of the date hereof and as they presently apply.

          (b) We express no opinion as to the effect of the laws of any state or
     jurisdiction other than the State of Illinois and the laws of the United
     States of America upon the transactions described herein.

          (c) In rendering the opinions set forth below, we have relied, to the
     extent we believe appropriate, as to matters of fact, (i) upon certificates
     or statements of public officials and of the officers of EQR, and (ii) upon
     representations and warranties




                                               ERP Operating Limited Partnership
                                                                   March 2, 2001
                                                                          Page 3


     contained in the Underwriting Agreement and the Registration Statement, and
     we have made no independent investigation or verification of said facts. No
     opinion is being expressed as to the effect of any event, fact or
     circumstance of which we have no actual knowledge.

          (d) We have assumed the competency of the signatories to the
     Underwriting Agreement, the global certificates representing the Notes and
     certain officers certificates, the genuineness of all signatures, 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 accuracy and completeness of all records made
     available to us.

          (e) We have assumed that (i) the Underwriting Agreement has been duly
     authorized, executed and delivered by the parties thereto (other than our
     client), is within their corporate, trust, limited liability company or
     partnership power, and are their legal, valid and binding obligation(s) and
     that it is in compliance with all applicable laws, rules and regulations
     governing the conduct of their respective businesses and this transaction,
     (ii) the Underwriting Agreement will be enforced in circumstances and in a
     manner which is commercially reasonable, (iii) the parties to the
     Underwriting Agreement (other than our client), are not subject to any
     statute, rule or regulation or any impediment that requires them or our
     client to obtain the consent, or to make any declaration or filing with any
     governmental authority in connection with the transactions contemplated by
     the Underwriting Agreement, and (iv) all terms, provisions and conditions
     relating to the transaction referred to in this opinion letter are
     correctly and completely reflected in the Underwriting Agreement.

          (f) The opinions hereafter expressed are qualified to the extent that:
     (i) the characterization of, and the enforceability of any rights or
     remedies in, any agreement or instrument may be limited by applicable
     bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance
     or transfer, equitable subordination, or similar laws and doctrines
     affecting the rights of creditors generally and general equitable
     principles; (ii) the availability of specific performance, injunctive
     relief or any other equitable remedy is subject to the discretion of a
     court of competent jurisdiction; and (iii) the provisions of any document,
     agreement or instrument that (a) may require indemnification or
     contribution for liabilities under the provisions of any Federal or state
     securities laws or in respect to the neglect or wrongful conduct of the
     indemnified party or its representatives or agents, (b) purport to confer,
     waive or consent to the jurisdiction of any court, or (c) waive any right
     granted by common or statutory law, may be unenforceable as against public
     policy; and (iv) any provisions of the Underwriting Agreement granting
     so-called "self-help" or extrajudicial remedies may not be enforceable.



                                               ERP Operating Limited Partnership
                                                                   March 2, 2001
                                                                          Page 4


          (g) Requirements in the Underwriting Agreement specifying that
     provisions thereof may only be waived in writing may not be valid, binding
     or enforceable to the extent that an oral agreement or an implied agreement
     by trade practice or course of conduct has been created modifying any
     provision of such documents.

          (h) Whenever our opinion, with respect to the existence or absence of
     facts, is qualified by the phrase "to our knowledge" or a phrase of similar
     import, it indicates that during the course of our representation of the
     Operating Partnership in connection with the subject transaction no
     information has come to the attention of our attorneys who have worked on
     the subject transaction which would give us current actual knowledge of the
     existence or absence of such facts. Without limiting the generality of
     the foregoing, it is expressly understood that no opinion is expressed
     with regard to: (a) the financial ability of the Operating Partnership
     to meet its obligations under either the Indenture dated October 1, 1994
     between the Operating Partnership and Bank One Trust Company, NA, as
     successor to the First National Bank of Chicago (the "Indenture") relating
     to the Notes or the Terms Agreement; (b) although we are not aware of
     any untruthfulness or inaccuracy, the truthfulness or accuracy of any
     applications, reports, plans, documents, financial statements or other
     matters furnished to the underwriters by (or on behalf of) the Operating
     Partnership in connection with the Indenture, the Terms Agreement or the
     Registration Statement; or (c) although we are not aware of any
     untruthfulness or inaccuracy, the truthfulness or accuracy of any
     representations or warranties made by the Operating Partnership in the
     Indenture, the Terms Agreement or the Registration Statement or other
     documents described herein, which are not the subject of any of the
     opinions stated herein. However, except to the extent expressly
     set forth herein, we have not undertaken any independent investigation to
     determine the existence or absence of such facts, and no inference as to
     our knowledge of the existence or absence of such facts should be drawn
     from the fact of our representation of the Operating Partnership or any
     other matter. To the extent that any member of this firm may be involved as
     a principal with any of the entities or in any of the transactions
     described herein, the knowledge of such person obtained in such capacity of
     any events, facts or circumstances shall not be imputed to us in our
     capacity as counsel.

          (i) We have examined the latest compilations that are available to us
     of the applicable statutes of such jurisdictions that relate to the
     issuance of the Notes and, in certain instances, the written regulations
     and rulings issued thereunder. We have not obtained special written rulings
     of the SEC, state securities commissions or other administrative bodies or
     officials charged with the administration of such statutes, regulations and
     rulings and we have not obtained and do not rely on opinions of other
     counsel.

     Based upon the foregoing, and in reliance thereon, but subject to the
assumptions, limitations and qualifications expressed herein, we are of the
opinion that, as of the date hereof, following issuance of the Notes pursuant to
the terms of the Underwriting Agreement and receipt by the Operating Partnership
of the consideration for the Notes specified in the resolutions of the Company's
Board of Trustees and the Pricing Committee referred to above, the Notes will be
validly issued and legally binding obligations of the Operating Partnership
enforceable against the Operating Partnership in accordance with their terms,
subject to applicable bankruptcy, insolvency, reorganization, moratorium,
fraudulent transfer, or similar laws affecting creditors' rights generally from
time to time in effect and general principles of equity (regardless of whether
such enforceability is considered in a proceeding at law or in equity) and
except that a waiver of rights under any usury law may be unenforceable.

     We assume no obligation to advise you of any changes in the foregoing
subsequent to the delivery of this opinion letter. This opinion letter has been
prepared solely for your use in



                                               ERP Operating Limited Partnership
                                                                   March 2, 2001
                                                                          Page 5

connection with the filing by the Operating Partnership of a Current Report on
Form 8-K on the date of this opinion letter, which Form 8-K will be incorporated
by reference into the Registration Statement. This opinion letter should not be
quoted in whole or in part or otherwise be referred to, nor filed with or
furnished to any governmental agency or other person or entity, without the
prior written consent of this firm.

     We hereby consent (i) to be named in the Registration Statement, and in the
Prospectus, as attorneys who will pass upon the legality of the Securities to be
sold thereunder and (ii) to the filing of this opinion as an Exhibit to the
Registration Statement. In giving this consent, we do not thereby admit that we
are an "expert" within the meaning of the Securities Act of 1933, as amended.

                                       Very truly yours,



                                       PIPER MARBURY RUDNICK & WOLFE