Li-air batteries have attracted attention as a next generation secondary battery because of their potentials such as a high theoretical specific energy density. One of the main issues for the Li-air batteries is the development of a cathode oxygen electrode with high capacity and charge-discharge cycle stability. Here we report a manganese oxide with a card-house-like structure for the cathode oxygen electrode. The manganese oxide was synthesized by reassembling two-dimensional manganese oxide nanosheets. The cathode electrode containing the manganese oxide exhibited high catalytic activity for Li+/Li2Ox (x = 1, 2) redox reactions, and its discharge capacity was 1300-1500 mAh g(-1) catalyst, which was higher than that of Li-air batteries using electrolytic MnO2 as catalysts. (C) 2011 Elsevier B.V. All rights reserved.