ZnS films are prepared on glass and quartz substrates by sulfidation of the ZnO films which are deposited via reactive magnetron sputtering and annealed under v arious conditions. The sulfurized films are characterized by using x_ray diffrac tion, scanning electron microscope and UV—VIS spectrometer. The results show t hat the crystalline structure and optical properties of the sulfurized films dep end on the annealing conditions. ZnO films annealed in vacuum and pure O2 2 at mosphere, respectively, are converted partially to the hexagonal ZnS, while the annealed ZnO films in air and pure N22, respectively, are converted t otally to ZnS. Also the ZnS films produced by sulfurizing the annealed ZnO films in air an d pure N22, respectively, have a high optical transmittance of about 80% at the wavelength of 400—800nm, with the band-gap energies of 366 and 361eV, respectively.