Nanostructured manganese dioxide (MnO2) was potentiodynamically deposited on polyaniline (PANI) matrix at a scan rate of 200 mV s(-1). The composite electrode of PANI and MnO2 (PANI-MnO2) was characterized in 0.1 M Na2SO4 for electrochemical supercapacitors. Optimization of thickness of the PANI film and the amount of MnO2 deposition were necessary to realize large specific capacitance values. A specific capacitance of 715 F g(-1) and an energy density of about 200 Wh kg(-1) was obtained at a charge/discharge current density of 5 mA cm(-2), based on the combined mass of PANI-MnO2. Long stability of the composite material was demonstrated. (C) 2004 The Electrochemical Society.