High-quality ZnO1-xSx thin films were grown on (001) sapphire substrates in the temperature range of 300-800 degrees C by pulsed laser deposition (PLO) with a ZnS ceramic target and O-2 as reactive gas. By increasing the substrate temperature, the crystalline quality of the films is enhanced. The S content in the single-phase ZnO1-xSx films can be systematically adjusted from 0.556 to 0.202 via changing the substrate temperature. The maximum S content in the film grown at 300 degrees C reaches 0.556 without phase separation, which is significantly higher than the solid solubility limits reported previously for the ZnOS alloys. The narrowed band gap of the ZnO1-xSx film (2.63 eV) grown at the low substrate temperature will extend the application of ZnO-based optoelectronic devices to the blue light region. As the composition, structure, and band gap energy of the ZnOS films were found to depend critically on the growth temperature, this work suggests a simple and flexible means of tuning the composition and optical band gap of ZnOS alloy films by controlling the substrate temperature during the PLO process.