Amorphous MnO2 was synthesized using the sol-gel method by reduction of NaMnO4 with solid fumaric acid. The synthesized product was characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, BET and chemical analysis. Electrochemical characterization was performed using cyclic voltammetry by a three electrode method, and aqueous NaCl, KCl, and Na2SO4 solutions were used as electrolytes. Prepared material remained amorphous until 400 degreesC and transformed to crystalline Mn2O3 at 500degreesC. The composition of prepared material was determined to be Na(0.25)MnO(2)(.)0.5H(2)O. A maximum capacitance of 110F/g was obtained at a scan rate of 5 mV/s in 2 M NaCl solution. MnO2 yielded almost the same capacitance in 2 M and I M NaCl electrolytes. The specific capacitance of MnO2 remained constant up to 800 cycles in I M NaCl electrolyte at 5 mV/s scan rate. (C) 2004 Elsevier B.V. All rights reserved.