Exhibit 5.1

ALSTON&BIRD LLP

One Atlantic Center

1201 West Peachtree Street

Atlanta, GA 30309-3424

404-881-7000

Fax: 404-881-7777

www.alston.com

December 19, 2011

Duke Realty Corporation

600 East 96th Street, Suite 100

Indianapolis, IN 46240

(File No. 333-160952)

Ladies and Gentlemen:

We have acted as counsel to Duke Realty Corporation, an Indiana corporation (the “Company”), and Duke Realty Limited Partnership, an Indiana limited partnership (the “Operating Partnership”, and together with the Company, the “Duke Entities”), in connection with the above referenced shelf registration statement (the “Registration Statement”) (as amended and supplemented from time to time and including the documents incorporated by reference therein) filed by the Duke Entities with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”).

We are furnishing this opinion letter to you pursuant to Item 16 of the Commission’s Form S-3 and Item 601(b)(5) of the Commission’s Regulation S-K, in connection with the resale of up to 2,065,337 shares (the “Shares”) of the Company’s common stock, par value $0.01 per share (the “Common Stock”) by certain selling shareholders pursuant to the Company’s prospectus, dated July 31, 2009 (the “Prospectus”), included in the Registration Statement, and the related prospectus supplement dated December 19, 2011 (the “Prospectus Supplement”).

In the capacity described above, we have considered such matters of law and of fact, including the examination of originals or copies, certified or otherwise identified to our satisfaction, of such records and documents of the Duke Entities, including, without limitation, resolutions adopted by the boards of directors or committees thereof, or other appropriate governing bodies or controlling entities of the Duke Entities and the organizational documents of the Duke Entities (in each case, as amended and/or restated), certificates of officers and representatives (who, in our judgment, are likely to know the facts upon which the opinion or confirmation will be based) of the Duke Entities, certificates of public officials, the Registration Statement (including the Prospectus Supplement contained therein) and such other documents as we have deemed appropriate as a basis for the opinion hereinafter set forth. We also have made such further legal and factual examinations and investigations as we deemed necessary for purposes of expressing the opinion set forth herein.

As to certain factual matters relevant to this opinion letter, we have relied upon the representations, warranties and statements made in originals or copies, certified or otherwise identified to our satisfaction, of such records, agreements, documents and instruments, including

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December 19, 2011

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certificates or comparable documents of officers of the Duke Entities and of public officials. Except to the extent expressly set forth herein, we have made no independent investigations with regard thereto, and, accordingly, we do not express any opinion or belief as to matters that might have been disclosed by independent verification.

In our examination of the relevant documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents and the conformity to authentic original documents of all documents submitted to us as copies (including telecopies). This opinion letter is given, and all statements herein are made, in the context of the foregoing.

Our opinion set forth below is limited to the laws of the Indiana Business Corporation Law, applicable provisions of the Constitution of the State of Indiana and reported judicial decisions interpreting such Corporation Law and Constitution that, in our professional judgment, are normally applicable to transactions of the type contemplated by the Registration Statement and the Prospectus Supplement, and federal laws of the United States of America to the extent referred to specifically herein, and we do not express any opinion herein concerning any other laws, statutes, ordinances, rules or regulations.

Based upon the foregoing, and subject, in all respects, to the assumptions, qualifications and limitations set forth in this opinion letter, it is our opinion that:

(1) The Shares are duly authorized, validly issued, fully paid and nonassessable.

This opinion letter is provided for use solely in connection with the registration and issuance of the Shares under the Registration Statement, the Prospectus and the Prospectus Supplement, and may not be used, circulated, quoted or otherwise relied upon for any other purpose without our prior express written consent. The only opinion rendered by us consists of those matters set forth in the paragraph numbered (1) above, and no opinion may be implied or inferred beyond the opinion expressly stated. Our opinion expressed herein is as of the date hereof, and we undertake no obligation to advise you of any changes in applicable law or any other matters that may come to our attention after the date hereof that may affect our opinion expressed herein.

December 19, 2011

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We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement (or the filing of this opinion as Exhibit 5.1 to a Current Report on Form 8-K, which will be incorporated by reference into the Registration Statement, as appropriate), and to the reference to this law firm under the caption “Legal Matters” in the Prospectus constituting a part of the Registration Statement. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Act or that we are otherwise within the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.