The basic character of NaX-type zeolites was systematically altered by incorporating nonframework K+, Rb+ and Cs+ cations with ([M]/([M]+[Na]) ca. similar to0.55). Correlation between activity and basicity was established. The role of Lewis basicity was found to be more important than the changes in specific area or micropore volume of different cation-exchanged samples in deciding the catalyst activity in the Knoevenagel condensation reaction. The catalyst activity was found to decrease with lowering the degree of crystallinity in the case of NaX zeolites.