Sm2O3 optical thin film is a new photovoltaic material and has potential applications in optical switches, date recording device and magnetic device. Using samarium dichloride as raw material, Sm2O3 optical thin films were prepared by sol-gel and hydrothermal process on glass and Si (100) substrates. The phase compositions, morphologies and optical properties of the as-prepared thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and UV-vis spectrophotometer (UV-vis). Results show that the Sm2O3 thin films prepared by sol-gel method exhibit an obvious (110) orientation growth on glass substrates, while the Sm2O3 thin films prepared with hydrothermal method have no obvious orientation. The as-prepared films have excellent absorbency of UV light and are transparent to visible light. The band gap of the Sm2O3 films prepared by hydrothermal method is narrower than that of those obtained by sol-gel method. The absorbency of UV light and transparence to visible of the Sm2O3 films prepared by sol-gel method are obviously improved in comparison with those deposited by hydrothermal process.