It has been found that the photocatalytic activity of TiO 2 toward the decomposition of 1,4-dichlorobenzene (DCB) aqueous solution can be greatly improved by loading WO 3 on the TiO 2 surface. In this work, we have investigated the role of WO 3 in enhancing the photocatalytic activity of TiO 2 . The surface structure of WO 3 /TiO 2 was characterized by surface acidity measurements and by surface analysis with XPS and TEM techniques. WO 3 covers the surface of TiO 2 with monolayer thickness and the WO 3 /TiO 2 particles are better able to disperse than the pure TiO 2 suspended in aqueous solution. The role of WO 3 in enhancing the photocatalytic activity of TiO 2 has been studied by utilizing the photocatalysts prepared in a film form. First, benzene and 2-propanol were used as gas-phase model compounds. WO 3 /TiO 2 demonstrates 3.6–5.9 times the photocatalytic activity of pure TiO 2 . Second, methylene blue coated on the photocatalysts was applied in the photocatalytic oxidation reaction. WO 3 /TiO 2 presents only 1.4–1.5 times the photocatalytic activity of pure TiO 2 in decomposing the coated methylene blue. Based upon these observations, the mechanistic role of WO 3 in the photocatalytic oxidation reaction has been suggested.