To meet the further requirements of using ZnS thin films in the field of optical films, ZnS thin films were grown on GaAs substrates at 130 ℃ by using DEZn and H2S as reaction sources on the basis of Atomic Layer Deposition (ALD). The surface morphology and interfacial properties of the samples were analyzed by Scanning Electron Microscopy (SEM). The structural properties of the thin films were analyzed by X-ray Diffractometer(XRD) and the chemical compositions of the thin films were analyzed by X-ray Photoelectron Spectroscopy (XPS). The effects of thickness on the structure and morphology of the thin films were studied. The results showed that the ZnS thin films obtained were polycrystalline. Their thickness increased linearly with the number of cycles at a rate of 1.45 ?/cycle. The XPS analysis of the thin films baked at 75 ℃ for 48 h gave the ratio of Zn/S 1.07:1, which indicated that the residual H2S in the films was removed after baking. The thinner films grown in less time had better surface flatness and denser structure.