Abstract: ZnS:Co thin films were grown on quartz substrates at different substrate temperatures. Evolutions of the films’ microstructure and optical properties as a function of substrate temperature were analyzed. The crystalline quality was promoted, and the films demonstrated increasing (111) preferred orientation with increasing substrate temperature. The band gap decreased when the substrate temperature was increased from 25 ℃ to 400 ℃, and then further increased to 800℃. The evolution of the band gap is associated with the quantum confinement effect. Moreover, the refractive index, extinction coefficient and dielectric constant of the films present an increasing tendency with the increase of substrate temperature. It is shown that superior microcrystal films can be obtained at temperatures higher than 400℃.