Exhibit 31.2
                         CERTIFICATIONS

I, Patrick W. Keene, certify that:

1.  I  have  reviewed this quarterly report on Form 10-Q  of  AEI
Income & Growth Fund XXI Limited Partnership;

2. Based on my knowledge, this report does not contain any untrue
statement  of  a material fact or omit to state a  material  fact
necessary  to  make  the  statements  made,  in  light   of   the
circumstances  under  which  such  statements  were   made,   not
misleading with respect to the period covered by this report;

3.  Based  on my knowledge, the financial statements,  and  other
financial information included in this report, fairly present  in
all  material  respects  the  financial  condition,  results   of
operations and cash flows of the registrant as of, and  for,  the
periods presented in this report;

4.   The  registrant's  other  certifying  officer  and   I   are
responsible for establishing and maintaining disclosure  controls
and  procedures (as defined in Exchange Act Rules  13a-15(e)  and
15d-15(e))  and  internal  control over financial  reporting  (as
defined  in Exchange Act Rules 13a-15(f) and 15d-15(f))  for  the
registrant and have:

   a) Designed such disclosure controls and procedures, or caused
such disclosure controls and procedures to be designed under  our
supervision, to ensure that material information relating to  the
registrant,  including  its consolidated  subsidiaries,  is  made
known  to us by others within those entities, particularly during
the period in which this report is being prepared;

   b) Designed such internal control over financial reporting, or
caused  such  internal  control over financial  reporting  to  be
designed  under our supervision, to provide reasonable  assurance
regarding  the  reliability  of  financial  reporting   and   the
preparation  of  financial statements for  external  purposes  in
accordance with generally accepted accounting principles;

   c)  Evaluated the effectiveness of the registrant's disclosure
controls  and  procedures  and  presented  in  this  report   our
conclusions  about  the effectiveness of the disclosure  controls
and  procedures,  as  of the end of the period  covered  by  this
report based on such evaluation; and

   d)  Disclosed  in  this report any change in the  registrant's
internal  control over financial reporting that  occurred  during
the  registrant's  most recent fiscal quarter  (the  registrant's
fourth  fiscal quarter in the case of an annual report) that  has
materially  affected,  or  is  reasonably  likely  to  materially
affect,   the   registrant's  internal  control  over   financial
reporting; and

5.   The  registrant's  other  certifying  officer  and  I   have
disclosed,  based  on  our  most recent  evaluation  of  internal
control  over  financial reporting, to the registrant's  auditors
and  the  audit committee of the registrant's board of  directors
(or persons performing the equivalent functions):

   a) All significant deficiencies and material weaknesses in the
design  or operation of internal control over financial reporting
which  are reasonably likely to adversely affect the registrant's
ability  to  record,  process,  summarize  and  report  financial
information; and

  b) Any fraud, whether or not material, that involves management
or   other  employees  who  have  a  significant  role   in   the
registrant's internal control over financial reporting.


Date: August 11, 2010       /s/ PATRICK W KEENE
                                Patrick W. Keene, Chief Financial Officer
                                AEI Fund Management XXI, Inc.
                                Managing General Partner