The precursor Sm(OH)3 of Sm2O3 was synthesized by homogeneous precipitation hydrothermal method using hexamethylenetetramine(C6H12N4) and hydrated samarium nitrate[Sm(NO3)3·6H2O] as raw materials. The optimum calcination temperature (800 °C)was derived from thermogravimetry (TG) analysis and X-ray powder diffraction (XRD). The Sm2O3 mirco/nano particles were then prepared by calcining the precursors at 800 °C. The structures, morphologies and size of the Sm2O3 mirco/nano particles were characterized by XRD, scanning electron microscope (SEM). The influences of reaction temperature and time on the size and shape of the products were investigated. The results showed that Sm2O3 micro/nano particles and its precursor Sm(OH)3 were cubic and hexagonal crystalline, respectively. With the increase of the reaction time, mirco/nano Sm2O3 sheet structure gradually self-assembled into three-dimensional spherical flowers. The size of the Sm2O3 micro/nano particles decreased as the temperature increased, and the Sm2O3 nano-sheet structure become thicker and more closer.