Hydrated sodium manganese oxide was synthesized by reducing permanganate ion using ethanol by a sol–gel method. By including acetylene black in the synthetic reaction, we obtained composite materials in which sodium manganese oxide hydrate particles were small and mixed well with the acetylene black. We evaluated those composites as a lithium battery cathode and found that they showed 170mAhg−1 under 5mAg−1 and 117mAhg−1 under 5Ag−1 on the basis of composite weight. This rapid discharge performance was probably caused by the favorable contact condition of the composite constituents.