The catalytic reaction of benzaldehyde with n-heptaldehyde was studied at 100-175 degreesC in a stirred batch autoclave reactor using mesoporous molecular sieve Al-MCM-41 supported MgO. Competitive reactions of cross- versus self-aldolization produce alpha -pentylcinnamaldehyde (alpha -P-C) and 2-pentyl-2-nonenal, respectively. Both reactions exhibit similar activation energies. Increasing the deposited amount of MgO on Al-MCM-41 enhances the catalyst base amount but diminishes the surface area. The conversion of n-heptaldehyde increases with catalyst base amount, reaction temperature and reaction time, whereas the alpha -P-C selectivity exhibits only small variation with reaction conditions. The catalytic activity of Al-MCM-41 is significantly enhanced by the deposition of MgO.