Photocatalytic degradation of 4-chlorophenol was studied using TiO2, Pt/TiO2, TiO2-SiO2, and Pt/TiO2-SiO2 prepared by the sol-gel method. The addition of Pt in TiO2 improved the catalytic activity and the highest activity was obtained with 1%Pt/TiO2. For TiO2-SiO2, the highest activity was achieved with 10%SiO2-TiO2 because of its highest adsorption capacity. Although 1% Pt or 10% Si in TiO2 improved the catalyst activity, the synergistic effect of adding both 1% Pt and 10% Si was not observed.