Manganese oxide was prepared at different pH and temperatures and then precipitated into activated carbon by the chemical impregnation method. Size distributions of manganese oxide sol were also measured by light scattering. The electrodes were annealed in nitrogen gas at different temperatures. In addition, electrochemical characterization was carried out using cyclic voltammetry (CV) at a scan rate of 25 mV s−1 and chronopotentiometry (CP) with constant-current (10 mA cm−2). Maximum capacitance of 461.3 F g−1 was obtained in a 0.1 M Na2SO4 solution for manganese oxide prepared under optimum conditions (pH = 13.11 and T = 25 ºC) and annealed at a temperature of 195 ºC. The manganese oxide particle size decreased with annealing. This probably leads to increased specific capacitance. Using X-ray photoelectron spectroscopy (XPS) the results reveal that manganese oxide species are transformed from hydroxide to oxide after annealing.