In this study, a photocatalyst S-doped WO3 was successfully synthesized by the hydrothermal method. The prepared undoped and S-doped WO3 samples were then characterized by XRD, SEM, XPS, and UV-vis DRS. The results showed that the band gap energy of S-doped WO3 was lower than that of the undoped WO3, which led to a better absorption of visible light. Furthermore, the results of XPS analysis suggested that the doping with S element resulted in an increase in lattice oxygen vacancies on the surface of S-WO3, which could effectively improve the photocatalytic activity. The photocatalytic performance of the S-WO3 samples were evaluated by the measurement of methylene blue (MB) degradation under visible light irradiation. The experimental results demonstrated that S-doped WO3 sample exhibited a much better photodegradation performance compared to undoped WO3, with the maximum MB removal efficiency of 78.7% for the 5% S-WO3 sample. Based on the above results, the mechanisms of photodegradation of MB by S-WO3 were discussed.