CdS thin films were successfully deposited onto glass substrates for the first time by the polyol method using cadmium acetate, thiourea and diethylene glycol as the raw materials. The effects of the deposition temperature from 120 to 200℃ in steps of 20℃ on the structure, morphology and optical properties of the resultant films were investigated. It was found that the crystallinity was improved and the value of the surface average roughness was decreased with increasing the deposition temperature. The average grain sizes of the CdS thin films were 77.16and 76.61 nm at 140 and 180 ℃, respectively. All samples showed excellent transmittance and the band gaps were found to reduce from 2.55 to 2.45 eV with the increase of the deposition temperature, which was attributed to the improvement of crystallinity.