ZnSe:Co thin films were grown on sapphire (Al2O3) substrates by pulsed laser deposition at different substrate temperature. Evolutions of the microstructure, morphology and optical properties of the ZnSe:Co thin films as a function of substrate temperature were analyzed. The results indicated that the crystalline quality was promoted and the films demonstrated increasing (111) preferred orientation with increasing substrate temperature. Excellent crystalline quality and (111) preferred oriented thin film was grown at substrate temperature of 800 degrees C. The refractive index and dielectric constant analyzed by the transmission spectra increased with elevating substrate temperature, which may be due to the promotion of the film packing density. The thin films with wider optical band gap in range of 2.73 eV to 3.27 eV were obtained in the experiment. The band gap decreased when the substrate temperature was increased from 25 degrees C to 600 degrees C, and then increased with a further increase of substrate temperature to 800 degrees C. The evolution of band gap associates with the quantum confinement effect.