Abstract: Current cathodic electrodeposition method was adopted to deposit SmS optical thin films on the surface of Si（100）and glass using SmCl₃·6H₂O and Na₂S₂O₃·5H₂O mixture solutions.The as-deposited thin films were characterized by X-ray diffraction（XRD）,atomic force microscopy（AFM）and ultraviolet spectrophotometer.The influence of Sm³⁺/S₂O₃^2- and pH value of the solution on the phase compositions of the films were investigated.Results show that smooth and dense SmS thin film with the thickness about 70nm can be obtained when Sm³⁺/S₂O₃^2-= 1:2 and pH=4.5.The prepared thin films possess an obvious（331）orientation.Transmittance analysis of the film coated glass shows that the prepared thin film exhibits strong absorption band at 290-300nm;the band gap of the thin film is about 3.6 eV.