It is highly desirable to improve the high voltage stabilities of cathode materials for Li-ion battery materials since it can deliver a higher reversible capacity at high cutoff voltage. Herein, we propose a novel facile strategy to generate La2O3-modified LiNi1/3Co1/3Mn1/3O2 with superior electrochemical performance in the voltage range of 2.5–4.5 V via a solid-state method. It can be observed that La2O3-modified LiNi1/3Co1/3Mn1/3O2 can greatly enhance the electrochemical performance due to the synergistic effect of ion doping and surface-modifying. La ions doping can alleviate the Li+/Ni2+ mixing, and substantially enhance the structure stability of LiNi1/3Co1/3Mn1/3O2 during charge/discharge cycles at high cutoff voltage. LaNi0.4Co0.6O3/LaMnO3.26 spreading on the surface layer is very useful in improving the diffusion of Li+ and inhibiting the particles from reacting with the electrolyte, enhancing the high voltage stabilities of the interface between electrode and electrolyte. The capacity retention of 0.7% (molar fraction) La2O3-modified LiNi1/3Co1/3Mn1/3O2 is 79.0% after 300 cycles compared to 61.7% for bare LiNi1/3Co1/3Mn1/3O2. And its discharge capacity at 10 C is 141.7 mAh g−1 in the voltage range of 2.5–4.5 V, which is higher than those of other samples. This work not only offers a facile novel strategy to achieve superior electrochemical performances of cathode materials but also presents some new insights into the stabilization mechanism of modified cathode materials during charge/discharge cycles or long-term storage at high cutoff voltage.