Layered manganese oxide (KxMnO2) powders were synthesized by simple decomposition of KMnO4 at 300-800 degreesC in air. These manganese oxides were characterized by powder X-ray diffractometry, atomic absorption spectrometry, chemical redox titration, and X-ray photoelectron spectroscopy. Their electrochemical performances for secondary lithium batteries were investigated in a LiClO4-propylene carbonate(PC) solution. After removing side products, which were water soluble, the KxMnO2 (x less than or equal to 0.484) cathode unerwent reversible electrochemical intercalation/deintercalation of lithium. When the KxMnO2 powders were synthesized at 300 degreesC and then, washed with water or acidic solution after the synthesis, they exhibited satisfactory behavior with a specific capacity of 130-140 mAh g(-1) in the region of 3 V vs. Li/Li+ for more than 20 cycles.