The electrochemical oxidation of dense Mn films is shown to occur through the following sequence of oxides: Mn to MnO to Mn3O4 to Mn2O3 to MnO2. X-ray photoelectron spectroscopy analysis reveals that at each stage, the manganese exists as a hydrated compound. Complete oxidation was shown to be necessary to maintain high capacitance values when utilized as a redox supercapacitor. Partial oxidation was shown to reduce the amount of MnO2 present in the film and the relative surface area of the film, thus having a negative effect on the capacitance. Efforts to improve the hydration of the films oxidized to 0.9 V using a dual current oxidation proved unsuccessful. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2130696] All rights reserved.