Cu(In1−xGax)(Se,S)2 (CIGSS) thin films were deposited using a single quaternary target of Cu(In0.75Ga0.25)Se2(CIGS) by rf magnetron sputtering, followed by sulfurization. The effects of substrate temperature and post-sulfurization on the properties of CIGSS films were investigated. As the substrate temperature increased, the crystallinity of the films increased significantly and the grain size also increased. Energy dispersive X-ray spectroscopy of CIGS films showed that Cu, Ga and Se contents approached the stoichiometry of CIGS films with increasing substrate temperature.Post-sulfurization of as-deposited CIGS films was carried out to improve their properties. The resultant CIGSS thin films revealed a noticeable increase in (112) peak for films deposited under 200°C, while the intensities of the (220)/(204) and (312)/(116) peaks increased as well. Grains with a size of approximately 100nm were grown after sulfurization. The results of EDX of CIGSS thin films after sulfurization indicated that the Cu content increased slightly and the Ga and (Se+S) contents decreased significantly. The band gaps of the films were also noticeably reduced after sulfurization. The carrier concentrations of the films after sulfurization decreased greatly at substrate temperatures below 400°C, while they showed little change at temperatures above 400°C. The resistivity of the films after sulfurization increased with increasing substrate temperature and showed little change at temperatures above 400°C. As a result, CIGS films were transformed to the chalcopyrite phase with well crystallized grains through sulfurization.