Abstract Orthorhombic type LiCoxMn1−xO2 (0 ≤ x ≤ 0.14) oxides have been synthesized by hydrothermal treatment of (CoxMn1−x)3O4 precursors and LiOH aqueous solution at 170 °C. As-synthesized powders showed well-ordered β-NaMnO2 structures, and the products were single crystalline particle oxides from TEM observations. The particle size decreased with increasing the amount of Co substituent. Much more improved capacity upon 100 cycling was clearly seen in orthorhombic LiCo0.1Mn0.9O2, comparing to orthorhombic LiMnO2.