Cerium based ZSM5 catalysts are used to study NO reduction with NH3 in the presence of oxygen with and without moisture. The Ce-ZSM5 was prepared by wet impregnation method and characterized by X-ray diffraction technique, BET surface and SEM. Ce-ZSM5 showed better NOx reduction than H-ZSM5 which is a poor catalyst for NOx reduction with NH3. The metal incorporation in H-ZSM5 has increased the catalytic activity. The catalytic activity showed significant difference in NOx conversion with and without moisture. The disperse Ce species are the active centers for the reduction of NO with NH3 in the presence of oxygen.