Exhibit 31.1
                       CERTIFICATIONS

I, Robert P. Johnson, 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/ ROBERT P JOHNSON
                                Robert P. Johnson, President
                                AEI Fund Management XXI, Inc.
                                Managing General Partner