Filed Pursuant to Rule 424(b)(3)

Registration No. 333-164703

KBS REAL ESTATE INVESTMENT TRUST III, INC.

SUPPLEMENT NO. 27 DATED MARCH 6, 2014

TO THE PROSPECTUS DATED FEBRUARY 6, 2013

This document supplements, and should be read in conjunction with, the prospectus of KBS Real Estate Investment Trust III, Inc. dated February 6, 2013, as supplemented by supplement no. 21 dated January 10, 2014, supplement no. 22 dated January 10, 2014, supplement no. 23 dated February 4, 2014, supplement no. 24 dated February 19, 2014, supplement no. 25 dated February 20, 2014 and supplement no. 26 dated March 3, 2014. As used herein, the terms “we,” “our” and “us” refer to KBS Real Estate Investment Trust III, Inc. and, as required by context, KBS Limited Partnership III, which we refer to as our “Operating Partnership,” and to their subsidiaries. Capitalized terms used in this supplement have the same meanings as set forth in the prospectus. The purpose of this supplement is to disclose an amendment to the advisory agreement.

Advisory Agreement Amendment

On March 5, 2014 we and our advisor, entered into an amendment to the advisory agreement between the parties. Pursuant to the amendment, with respect to asset management fees accruing from March 1, 2014, our advisor defers, without interest, our obligation to pay asset management fees for any month in which our modified funds from operations (“MFFO”) for such month, as such term is defined in the practice guideline issued by the Investment Program Association (“IPA”) in November 2010 and interpreted by us, excluding asset management fees, does not exceed the amount of distributions declared by us for record dates of that month. We remain obligated to pay our advisor an asset management fee in any month in which our MFFO, excluding asset management fees, for such month exceeds the amount of distributions declared for the record dates of that month (such excess amount, an “MFFO Surplus”); however, any amount of such asset management fee in excess of the MFFO Surplus will also be deferred under the amendment. If the MFFO Surplus for any month exceeds the amount of the asset management fee payable for such month, any remaining MFFO Surplus will be applied to pay any asset management fee amounts previously deferred in accordance with this amendment.

However, notwithstanding the foregoing, any and all deferred asset management fees that are unpaid will become immediately due and payable at such time as our stockholders have received, together as a collective group, aggregate distributions (including distributions that may constitute a return of capital for federal income tax purposes) sufficient to provide (i) an 8.0% per year cumulative, noncompounded return on such net invested capital (the “Stockholders’ 8% Return”) and (ii) a return of their net invested capital, or the amount calculated by multiplying the total number of shares purchased by stockholders by the issue price, reduced by any amounts to repurchase shares pursuant to our share redemption program. The Stockholders’ 8% Return is not based on the return provided to any individual stockholder. Accordingly, it is not necessary for each of our stockholders to have received any minimum return in order for our advisor to receive deferred asset management fees.

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