Tungsten oxide (WOx) is expected to act as a photocatalytic material under visible light. We have deposited WOx thin films using radiofrequency sputtering and evaluated the photocatalytic activities of the films via degradation of methylene blue solution. The optical absorbance, crystallization, and surface morphology of the WOx thin films were also investigated. The absorption edge of the WOx thin films improved when the substrate temperature was high and the O2 gas flow rate was low. Crystallization proceeded when the substrate temperature was high and additional WOx diffraction peaks were appearing with low O2 gas flow during growth. Furthermore, the grain size of the WOx thin films was smaller when the O2 gas flow was high. The photocatalytic activity was higher when the substrate temperature and O2 gas flow rate were low.