The specific discharge capacity of gamma-MnO2 was improved with chemical oxidation and vacuum-drying processes. The intergrowth structure and electrochemical performance were studied by X-ray diffraction and electrochemical measurements; the structure-electrochemical property relationships were clarified. Vacuum-dried gamma-MnO2 showed structural changes with capacity fade as the temperature increased, while the chemically oxidized gamma-MnO2 showed no structural change without any capacity fading. The latter material showed a first discharge capacity of 275 mAh g(-1), and a reversible capacity of 250 mAh g(-1) with two discharge plateaux after second cycle, which is the highest capacity among the gamma-MnO2 prepared previously. (C) 2007 Elsevier B.V. All rights reserved.