The dependence on morphology of the supercapacitive characteristics of manganese dioxide nanospheres (NSs) and nanorods (NRs) was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and a series of electrochemical techniques. Because the nanosized pores in MnO2 NSs resulted in high surface area, MnO2 electrodes made of NSs had higher specific capacitance (SC) than those made of NRs at current densities less than 2.0 A g−1. However, at current densities over 2.0 A g−1, the power density of MnO2 electrodes composed of NRs was better than that of NSs. The high surface area and nanosized pores in MnO2 NSs increase the number of redox active sites, which leads to high specific capacitance. On the other hand, the small pore size in MnO2 NSs restricts the rates of charge and discharge, thus limiting their power density.