Exhibit 32

CERTIFICATION PURSUANT TO

18 U.S.C. §1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of AEI Income & Growth Fund XXI Limited Partnership (the “Partnership”) on Form 10-Q for the period ended March 31, 2013, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, Robert P. Johnson, President of AEI Fund Management XXI, Inc., the Managing General Partner of the Partnership, and Patrick W. Keene, Chief Financial Officer of AEI Fund Management XXI, Inc., each certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

1. The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Partnership.

/s/ ROBERT P JOHNSON

Robert P. Johnson, President

AEI Fund Management XXI, Inc.

Managing General Partner

May 13, 2013

/s/ PATRICK W KEENE

Patrick W. Keene, Chief Financial Officer

AEI Fund Management XXI, Inc.

Managing General Partner

May 13, 2013