A novel environmental friendly catalyst, H3PW12O40/MCM-48, was prepared by impregnation method. The catalysts were characterized by means of XRD and FT-IR. The synthesis of n-butyl methacrylate catalyzed by H3PW12O40/MCM-48 was studied with methacrylic acid and n-butyl alcohol as reactants. H3PW12O40/MCM-48 is an excellent catalyst for synthesizing n-butyl methacrylate and Keggin structure of H3PW12O40 kept unchanged after being impregnated on surface of the molecular sieve support. Effects of n (methacrylic acid): n (n-butyl alcohol), catalyst dosage, cyclohexane (water-stripped reagent) and reaction time on yields of the product were investigated. The optimum conditions have been found, that is, molar ratio of acid to alcohol is 1:1.6, mass ratio of catalyst used to the reactants is 0.5% and reaction time is 2.0h. Under these conditions, the yield of n-butyl methacrylate can reach 93.7%.