An orthorhombic LiMnO2 having a high capacity was hydrothermally synthesized at 170 degreesC from Mn3O4 obtained through autoxidation route. The LiMnO2/Li cell demonstrated the initial reversible capacities of about 210 mAh (g-oxide)(-1) at 30 degreesC. After several initial cycling, the cell showed stabilized cycling behavior (175 mAh g(-1) at the 30th cycle). We believe that orthorhombic LiMnO2 prepared by a new hydrothermal condition is an excellent candidate for the cathode of coming generation of high capacity material to be applied for lithium-ion secondary battery.