MnO2 samples are synthesized by an electrodeposition technique at a fixed pH and are tested as active electrode material for ail electrochemical supercapacitor. The physicochemical properties of electrolytic manganese dioxide, including average Mn oxidation state, amount of incorporated water, porosity, crystal structure, morphology, and electrochemical performance, are characterized. The characterization is carried Out by thermal gravimetry, composition analysis, the Barrett-Joyner-Halenda model, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry methods. The correlation between these properties and the deposition conditions (pH) is studied. The results show that the pH strongly influences the properties and, consequently, the activity of MnO2 in in electrochemical supercapacitor. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3184344] All rights reserved.