Sm2O3-modified Li[Li0.2Mn0.56Ni0.16Co0.08]O2 was synthesized via a simple wet chemical process followed by a solid state reaction. A thin Sm2O3 layer with a thickness of about 2.5nm was uniformly coated on the surface of the Li-rich layered oxide particles. After Sm2O3 surface modification, high discharge capacity of 214.6mAhg−1 with a retention of 91.5% is obtained at a current density of 200mAg−1 between 2.0V and 4.8V after 80 cycles. Electrochemical impedance spectroscopy (EIS) shows that the thin Sm2O3 layer mainly reduces the charge transfer resistance and stabilizes the surface structure of the active material during cycling. Sm2O3 modification will be a promising approach to improve the cyclic stability of Li-rich layered oxides.