Propylsulfonic acid functionalized silica (SFS) catalysts with varying amounts of surface propylsulfonic acid species (PrSA) and acidity were synthesized and characterized. The aldol condensation of benzaldehyde and n-heptanal over SFS catalysts was studied as a model reaction (which involves cross and self condensation reactions) to investigate the role of surface PrSA species in the cross condensation. The reaction temperature, reactant molar ratio and solvent nature (polar/non-polar) were found to be major reaction parameters controlling the cross and self aldol product selectivity. It was observed that the characteristics of carbonyl substrates influence their reactivity towards cross and self condensation over SFS catalyst.