Manganese dioxide shows an ideal capacitive behavior in the aqueous solution containing bivalent cations (Ca2+). A specific capacitance value as high as 310 F g(-1) in 0.1 mol L-1 Ca(NO3)(2) electrolyte was measured at a sweep rate of 2 mV s(-1). A cycle life test was also performed and no capacity loss of MnO2 electrode was found after 600 cycles, which indicates the MnO2 electrode possesses a good cycling property in the aqueous electrolyte containing bivalent cations (Ca2+). X-ray photoelectron spectroscopy data reveal that the Ca2+ ions in the electrolyte are involved in the charge storage process of manganese dioxide in an aqueous system and correspondingly a part of Mn4+ ions will become to Mn3+ ion to balance the charge.