NaY and KL zeolites were modified by impregnating with potassium fluoride for investigating their basicity and catalytic activity towards Henry nitroaldol reaction under different reaction conditions. Effects of solvents, temperature, catalysts and ratio of substrate versus reagents were studied to optimize the reaction conditions. The catalysts were characterized by FTIR, XRD and SEM techniques and the products were characterized by H-1 NMR, C-13 NMR and FTIR techniques. It was observed that NaY/KF zeolite with H2O-MeOH pair as solvent showed good conversion and selectivity at room temperature. Both XRD and FTIR study showed no change of spectral patterns for both modified and parent zeolites. We have again showed a plot of Hammett free energy linear relationship in terms of percentage yield and Hammett substituent constant. (C) 2012 Elsevier B.V. All rights reserved.