Heterogeneous photocatalysts consisting of phosphotungstic acid or silicotungstic acid immolilized on mesoporous molecular sieve MCM-41 were prepared and characterized by FTIR, X-ray diffraction, nitrogen adsorption and high resolution transmission electron microscope (HRTEM). The photocatalytic activities of the prepared H3PW12O40/MCM-41 or H4SiW12O40/MCM-41 were examined by photodegradation of pesticide paraquat. Results show that the prepared composites have large specific surface area and uniform mesopores, the Keggin structure of two parent heteropoly acids was retained after loading on MCM-41. Both of the prepared photocatalysts exhibit high activityies under irradiation of 365 nm monochromatic Light. For 50 mL paraquat (10 mg·L-1), conversions of paraquat using 15 mg H3PW12O40/MCM-41 or H4SiW12O40/MCM-41 as catalysts after 14 hours’ irradiation are 92.0% and 87.6% respectively. The photocatalytic reactions are in accordance with the first order kinetics equation, and the half lives of the reactions are 3.6 h and 4.7 h respectively.