Nanosized LiMnO2-LiMnO3 compounds were synthesized by a hydrothermal method. The contents of Li2MnO3 and LiMnO2 in these compounds vary with the employed molar ratio of starting materials [i.e., (NH4)(2)S2O8/MnSO4]. The effects of the reaction time and temperature on the hydrothermal products were investigated. The hydrothermally prepared LiMnO2-Li2MnO3 compounds have higher electrochemical activities compared to those obtained from conventional solid-state reaction at high temperature [e.g., during the initial discharging process at 20 mA g(-1), o-LiMnO2 (sample LMO-1) and Li2MnO3 (sample LMO-4) delivered at 184 and 247 mAh respectively]. Meanwhile, such nanosized compounds exhibited good rate capabilities (e.g., at a current density of 200 mA g(-1), sample LMO-4 delivered a capacity of 208 mAh g(-1), 84% of that obtained at 20 mA g(-1)). Comparison of electrochemical performances among the four nanosized compounds obtained from our hydrothermal conditions indicates that the Li2MnO3 has the higher discharge capacity while the o-LiMnO2 shows the better cyclability. (C) 2009 The Electrochemical Society.