A lithium-manganese oxide, LixMnO2 (x = 0.3-0.6), has been synthesized by heating a mixture (Li/Mn ratio = 0.3-0.8) of electrolytic manganese dioxide (EMD) and LiNO3 in air at moderate temperature, 260 °C. The formation of the Li-Mn-O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li-Mn-O were examined in LiClO4-propylene carbonate electrolyte solution. About 0.3 Li in LixMnO2 (x = 0.3-0.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5 V and 2.8 V vs Li/Li+. The LixMnO2 synthesized by heating at Li/Mn ratio = 0.5 demonstrated higher discharge capacity, about 250 mAh (g of oxide)-1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.