Li-rich layered oxides show high reversible capacities (≥250mAh/g) in rechargeable lithium-ion batteries. However, their energy densities are considerably reduced upon cycling due to a voltage depression originated from the layered-to-spinel phase transition. In this study, the influence of site-specific Ga-doping on the electrochemical properties of Li-rich layered oxide is investigated. A powder of Li-rich layered oxide is treated in acid, and then annealed with a Ga source at low temperature (300°C) to insert Ga ions into the powder. Transmission electron microscopy and extended X-ray absorption fine structure analyses indicate that the Ga ions are predominantly doped into the tetrahedral sites of Li2MnO3-like nano-domains in Li-rich layered oxide. Cyclability tests with 18650 full cells clearly reveal that the voltage depression is suppressed by the treatment. Ex-situ X-ray diffraction and first principles calculation results imply that the formation of tetrahedral GaO4 unit in the Li2MnO3-like domain improves the structural stability of Li-rich layered oxide upon cycling.