Y2O3:Sm and Gd2O3:Sm powder phosphors were prepared by carbonate coprecipitation method. The purified crystalline phases of Y2O3:Sm and Gd2O3:Sm were obtained at 600°C, and the crystallinity increases with increase in annealing temperature. Both samples contain aggregated phosphor particles. An energy transfer (ET) from Y2O3 and Gd2O3 hosts to sm3+ has been observed, and the ET efficiency in the latter is higher than that in the former because an energy migration process like Gd3+–(Gd3+)n–Sm3+ has occurred in the latter. Furthermore, an upconversion luminescence from the 4G5/2 level of Sm3+ has been observed in both Y2O3 and Gd2O3 under the excitation of 936nm infrared, whose mechanisms are proposed. Both the up and downconversion emission intensities of Sm3+ in Gd2O3 are stronger than those in Y2O3.