A sulfur (S)-doped titanium dioxide (TiO2) photocatalyst was synthesized by oxidative annealing of titanium disulfide (TiS2). TiS2 turned into anatase TiO2 when annealed in air. The residual S atoms occupied O-atom sites in the TiO2 to form Ti-S bonds. The S doping caused the absorption edge of TiO2 to be shifted into the lower energy region. Consequently, methylene blue adsorbed on the S-doped TiO2 was photocatalytically decomposed by visible light irradiation.