Highly efficient photocatalytic reduction of CO2 is essential for solving the greenhouse effect and energy crisis. In this paper, the Sm-TiO2 nanocomposites were successfully prepared via sol-gel method. The CO2 photoreduction activities of synthesized samples were tested under irradiation for 6 h and the results indicate that the 0.5％Sm-TiO2 catalyst has superior performance and stability. The CO and CH4 yields of 0.5％Sm-TiO2 catalyst are 55.47 and 3.82μmol/g·cat respectively, which are 5.02 and 2.67 times the yield of TiO2. The possible mechanism of Sm doped TiO2 was investigated through comprehensive charac-terization and photoelectrochemical analysis. After the Sm doping, the photo-generated electrons in TiO2 could migrate to Sm 4f, and some of them can be captured by reducing Sm3+to Sm2+, which can lower the recombination rate of electron and hole pairs. Therefore, the enhanced photocatalytic performance could be ascribed to large specific surface area, fast separation rate of electron-hole pairs and high visible light response. This report provides some meaningful attempts in researching the CO2 photo-catalytic reduction.