Nanosized photocatalyst ZnS particles supported on silica and polyvinyl alcohol was successfully prepared by complex trans-formation method. The photoc^jtic reduction of CO2 was carried out in the presence of nanosized ZnS catalyst irradiated by a high-pressure mercury-vapor lamp to give the main products of formaldehyde and ethanol. The catalytic ability of ZnS characterized by the uptaken rate of CO2 volume in the reaction system depended upon the preparing conditions of nanosized ZnS catalysts. Decreasing the concentration of Na2 S and increasing the molar ratio of oxygen in the PVA to Zn^2 + could result in the decreasing of the size of ZnS particles but could not result in the monotonous increasing of the reduction rate of CO2. The mechanism of reduction of CO2 may be related to the H atoms and OH radicals, which form from H2O by transmission of the electron-hole pairs from irradiated the naaosized ZnS.
