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°C and transformed to crystalline Mn2O3 at 500°C. The composition of prepared material was determined to be Na0.25MnO2·0.5H2O. A maximum capacitance of 110F/g was obtained at a scan rate of 5mV/s in 2M NaCl solution. MnO2 yielded almost the same capacitance in 2M and 1M NaCl electrolytes. The specific capacitance of MnO2 remained constant up to 800cycles in 1M NaCl electrolyte at 5mV/s scan rate.