A novel photocatalyst, carbon-sulfur-codoped TiO2 (TCS) was synthesized by the hydrolysis of tetrabutyl titanate in a mixed aqueous solution containing thiourea and urea. The codoped TiO2 was also prepared directly by calcining amorphous or anatase TiO2 with a mixture of thiourea and urea. The as-prepared powders were characterized by X-ray diffraction (XRD), UV-visible reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and thermal analysis-thermogravimetry (TG-DSC). The photocatalytic activity was evaluated by the photodegradation of 4-chlorophenol under both UV and visible irradiation. By investigating the crystal structures, optical properties, and photocatalytic activities of various samples, we found that the wet chemistry process and the crystal transition process from amorphous to anatase seemed to be critical to the doping process.