Exhibit 10.6

Loan No. 10032921

GUARANTY AGREEMENT

THIS GUARANTY AGREEMENT (this “ Guaranty ”) is executed as of November 30, 2006, by BEHRINGER HARVARD REIT I, INC ., a Maryland corporation, having an address c/o Behringer Harvard Funds, 15601 Dallas Parkway, Suite 600, Addison, Texas 75001 (whether one or more collectively referred to as “Guarantor” ), for the benefit of KEYBANK NATIONAL ASSOCIATION , a national association, having an office at 911 Main Street, Suite 1500, Kansas City, MO 64105 (together with its successors and/or assignors “ Lender ”).

W I T N E S S E T H:

WHEREAS , pursuant to that certain Promissory Note, dated the date hereof, executed by BEHRINGER HARVARD 945 EAST PACES FERRY ROAD, LLC , a Delaware limited liability company (“ Borrower ”), and payable to the order of Lender in the original principal amount of EIGHTY-TWO MILLION and No/100 DOLLARS ($82,000,000.00) (as the same may hereafter be amended, restated, renewed, supplemented, replaced, extended or otherwise modified from time to time, the “ Note ”), Borrower has become indebted, and may from time to time be further indebted, to Lender with respect to a loan (the “ Loan ”) which is secured by the lien and security interest of that certain Fee and Leasehold Deed to Secure Debt and Security Agreement, dated as of the date hereof, made by Borrower for the benefit of Lender (as the same may hereafter be amended, restated, renewed, supplemented, replaced, extended or otherwise modified from time to time, the “ Security Instrument ”), and is further evidenced by that certain Loan Agreement, dated as of the date hereof, between Borrower and Lender (as the same may hereinafter be amended, modified, restated, renewed or replaced the “ Loan Agreement ”) and further evidenced, secured or governed by such other instruments and documents executed in connection with the Loan (together with the Note, the Loan Agreement and the Security Instrument are hereinafter collectively referred to as the “ Loan Documents ”); and

WHEREAS , Lender is not willing to make the Loan, or otherwise extend credit, to Borrower unless Guarantor unconditionally guarantees payment and performance to Lender of the Guaranteed Obligations (as herein defined); and

WHEREAS , Guarantor is the owner of a direct or indirect interest in Borrower, and Guarantor will directly benefit from Lender’s making the Loan to Borrower.

NOW, THEREFORE , as an inducement to Lender to make the Loan to Borrower, and to extend such additional credit as Lender may from time to time agree to extend under the Loan Documents, and for other good and valuable consideration, the receipt and legal sufficiency of which are hereby acknowledged, the parties do hereby agree as follows:

ARTICLE I.

NATURE AND SCOPE OF GUARANTY

Section 1.01         Guaranty Of Obligation .  Guarantor hereby irrevocably and unconditionally guarantees to Lender and its successors and assigns the payment and performance of the Guaranteed Obligations as and when the same shall be due and payable, whether by lapse of time, by acceleration of maturity or otherwise.  Guarantor hereby irrevocably and unconditionally covenants and agrees that it is liable for the Guaranteed Obligations as a primary obligor.

Section 1.02         Definition of Guaranteed Obligations .  As used herein, the term “Guaranteed Obligations” shall (i) mean each of the obligations of Borrower under the Environmental Indemnity, including without limitation the indemnification provisions contained therein, and (ii) be deemed to include, and Guarantor shall also be liable for, and shall indemnify, defend and hold Lender harmless from and against, any and all Losses (as hereinafter defined) incurred or suffered by Lender and arising out of or in connection with the matters listed below:

(a)           the misapplication or misappropriation of Rents;

(b)           the misapplication or misappropriation of Insurance Proceeds or Awards;

(c)           Borrower’s failure to return or to reimburse Lender for all Personal Property (other than Personal Property not material to the operation or value of the affected Individual Property) taken from the Property by or on behalf of Borrower and not replaced with Personal Property of the same utility and of the same or greater value;

(d)           any act of actual waste or arson by Borrower, any principal, affiliate, general partner or member thereof or by Guarantor;

(e)           any fees or commissions paid by Borrower to any principal, affiliate, general partner or member of Borrower or any Guarantor in violation of the terms of this Guaranty, the other Loan Documents;

(f)            Borrower’s failure to comply with the provisions of Section 9.4 of the Security Instrument;

(g)           any fraud, willful misconduct or intentional material misrepresentation by Borrower, Principal, Guarantor or any of their respective Affiliates in connection with the Loan; or

(h)           any breach or default of any material provision of Section 4.1.30 of the Loan Agreement (other than breaches of the requirements set forth in clauses (xii) or (xxiii) of the definition of Special Purpose Entity).

2

(iii)          In addition, the Guaranteed Obligations shall also include the unpaid balance of the Debt in the event of: (a) a voluntary breach or default under Section 5.2.10 of the Loan Agreement, (b) Borrower or Principal filing a voluntary petition under the Bankruptcy Code or any other Federal or state bankruptcy or insolvency law; (c) Borrower or Principal filing an answer consenting to or otherwise acquiescing in or joining in any involuntary petition filed against it, by any other Person under the Bankruptcy Code or any other Federal or state bankruptcy or insolvency law, or soliciting or causing to be solicited petitioning creditors for any involuntary petition from any Person; (d) Borrower or Principal consenting to or acquiescing in or joining in an application for the appointment of a custodian, receiver, trustee, or examiner for Borrower, Principal or any portion of the Property; or (e) Borrower or Principal making an assignment for the benefit of creditors.

Section 1.03         Nature of Guaranty .  This Guaranty is an irrevocable, absolute, continuing guaranty of payment and performance and not a guaranty of collection.  This Guaranty may not be revoked by Guarantor and shall continue to be effective with respect to any Guaranteed Obligations arising or created after any attempted revocation by Guarantor and after (if Guarantor is a natural person) Guarantor’s death (in which event this Guaranty shall be binding upon Guarantor’s estate and Guarantor’s legal representatives and heirs).  The fact that at any time or from time to time the Guaranteed Obligations may be increased or reduced shall not release or discharge the obligation of Guarantor to Lender with respect to the Guaranteed Obligations.  This Guaranty may be enforced by Lender and any subsequent holder of the Note and shall not be discharged by the assignment or negotiation of all or part of the Note.

Section 1.04         Guaranteed Obligations Not Reduced by Offset .  The Guaranteed Obligations and the liabilities and obligations of Guarantor to Lender hereunder, shall not be reduced, discharged or released because or by reason of any existing or future offset, claim or defense of Borrower, or any other party, against Lender or against payment of the Guaranteed Obligations, whether such offset, claim or defense arises in connection with the Guaranteed Obligations (or the transactions creating the Guaranteed Obligations) or otherwise.

Section 1.05         Payment By Guarantor .  If all or any part of the Guaranteed Obligations shall not be punctually paid when due, whether at demand, maturity, acceleration or otherwise, Guarantor shall, immediately upon demand by Lender, and without presentment, protest, notice of protest, notice of non-payment, notice of intention to accelerate the maturity, notice of acceleration of the maturity, or any other notice whatsoever, pay in lawful money of the United States of America, the amount due on the Guaranteed Obligations to Lender at Lender’s address as set forth herein.  Such demand(s) may be made at any time coincident with or after the time for payment of all or part of the Guaranteed Obligations, and may be made from time to time with respect to the same or different items of Guaranteed Obligations.  Such demand shall be deemed made, given and received in accordance with the notice provisions hereof.

3

Section 1.06         No Duty To Pursue Others .  It shall not be necessary for Lender (and Guarantor hereby waives any rights which Guarantor may have to require Lender), in order to enforce the obligations of Guarantor hereunder, first to (i) institute suit or exhaust its remedies against Borrower or others liable on the Loan or the Guaranteed Obligations or any other person, (ii) enforce Lender’s rights against any collateral which shall ever have been given to secure the Loan, (iii) enforce Lender’s rights against any other guarantors of the Guaranteed Obligations, (iv) join Borrower or any others liable on the Guaranteed Obligations in any action seeking to enforce this Guaranty, (v) exhaust any remedies available to Lender against any collateral which shall ever have been given to secure the Loan, or (vi) resort to any other means of obtaining payment of the Guaranteed Obligations. Lender shall not be required to mitigate damages or take any other action to reduce, collect or enforce the Guaranteed Obligations.

Section 1.07         Waivers .  Guarantor agrees to the provisions of the Loan Documents, and hereby waives notice of (i) any loans or advances made by Lender to Borrower, (ii) acceptance of this Guaranty, (iii) any amendment or extension of the Note, the Security Instrument, the Loan Agreement or of any other Loan Documents, (iv) the execution and delivery by Borrower and Lender of any other loan or credit agreement or of Borrower’s execution and delivery of any promissory notes or other documents arising under the Loan Documents or in connection with the Property, (v) the occurrence of any breach by Borrower or an Event of Default, (vi) Lender’s transfer or disposition of the Guaranteed Obligations, or any part thereof, (vii) sale or foreclosure (or posting or advertising for sale or foreclosure) of any collateral for the Guaranteed Obligations, (viii) protest, proof of non-payment or default by Borrower, or (ix) any other action at any time taken or omitted by Lender, and, generally, all demands and notices of every kind in connection with this Guaranty, the Loan Documents, any documents or agreements evidencing, securing or relating to any of the Guaranteed Obligations and the obligations hereby guaranteed.

Section 1.08         Payment of Expenses .  In the event that Guarantor should breach or fail to timely perform any provisions of this Guaranty, Guarantor shall, immediately upon demand by Lender, pay Lender all costs and expenses (including court costs and attorneys’ fees) incurred by Lender in the enforcement hereof or the preservation of Lender’s rights hereunder.  The covenant contained in this Section shall survive the payment and performance of the Guaranteed Obligations.

Section 1.09         Effect of Bankruptcy .  In the event that, pursuant to any insolvency, bankruptcy, reorganization, receivership or other debtor relief law, or any judgment, order or decision thereunder, Lender must rescind or restore any payment, or any part thereof, received by Lender in satisfaction of the Guaranteed Obligations, as set forth herein, any prior release or discharge from the terms of this Guaranty given to Guarantor by Lender shall be without effect, and this Guaranty shall remain in full force and effect. It is the intention of Borrower and Guarantor that Guarantor’s obligations hereunder shall not be discharged except by Guarantor’s performance of such obligations and then only to the extent of such performance.

4

Section 1.10         Waiver of Subrogation, Reimbursement and Contribution .  Guarantor hereby unconditionally and irrevocably waives, releases and abrogates any and all rights it may now or hereafter have under any agreement, at law or in equity (including, without limitation, any law subrogating the Guarantor to the rights of Lender), to assert any claim against or seek contribution, indemnification or any other form of reimbursement from Borrower or any other party liable for payment of any or all of the Guaranteed Obligations for any payment made by Guarantor under or in connection with this Guaranty or otherwise; provided, however, that notwithstanding anything to the contrary contained herein, Guarantor shall have and be entitled to (a) all rights of subrogation otherwise provided by applicable law in respect of any payment it may make or be obligated to make under this Guaranty and (b) all claims it would have against Borrower or any other party and to assert and enforce same, in each case on and after, but at no time prior to, the date which is 91 days after the date on which all sums owed to Lender under this Guaranty and the other the Loan Documents have been paid in full.

Section 1.11         Borrower .  The term “Borrower” as used herein shall include any new or successor corporation, association, partnership (general or limited), limited liability company, joint venture, trust or other individual or organization formed as a result of any merger, reorganization, sale, transfer, devise, gift or bequest of Borrower or any interest in Borrower.

ARTICLE II.

EVENTS AND CIRCUMSTANCES NOT REDUCING
OR DISCHARGING GUARANTOR’S OBLIGATIONS

Guarantor hereby consents and agrees to each of the following, and agrees that Guarantor’s obligations under this Guaranty shall not be released, diminished, impaired, reduced or adversely affected by any of the following, and waives any common law, equitable, statutory or other rights (including without limitation rights to notice) which Guarantor might otherwise have as a result of or in connection with any of the following:

Section 2.01         Modifications .  Any renewal, extension, increase, modification, alteration or rearrangement of all or any part of the Guaranteed Obligations, the Note, the Security Instrument, the Loan Agreement, the other Loan Documents, or any other document, instrument, contract or understanding between Borrower and Lender, or any other parties, pertaining to the Guaranteed Obligations or any failure of Lender to notify Guarantor of any such action.

Section 2.02         Adjustment .  Any adjustment, indulgence, forbearance or compromise that might be granted or given by Lender to Borrower or any other guarantor.

Section 2.03         Condition of Borrower or Guarantor .  The insolvency, bankruptcy, arrangement, adjustment, composition, liquidation, disability, dissolution or

5

lack of power of Borrower, Guarantor or any other party at any time liable for the payment of all or part of the Guaranteed Obligations; or any dissolution of Borrower or Guarantor, or any sale, lease or transfer of any or all of the assets of Borrower or Guarantor, or any changes in the shareholders, partners or members of Borrower or Guarantor; or any reorganization of Borrower or Guarantor.

Section 2.04         Invalidity of Guaranteed Obligations .  The invalidity, illegality or unenforceability of all or any part of the Guaranteed Obligations, or any document or agreement executed in connection with the Guaranteed Obligations, for any reason whatsoever, including without limitation the fact that (i) the Guaranteed Obligations, or any part thereo