Birnessite-type manganese dioxide (MnO2) is coated uniformly on carbon nanotubes (CNTs) by employing a spontaneous direct redox reaction between the CNTs and permanganate ions (MnO4 −). The initial specific capacitance of the MnO2/CNT nanocomposite in an organic electrolyte at a large current density of 1Ag−1 is 250Fg−1. This is equivalent to 139mAhg−1 based on the total weight of the electrode material that includes the electroactive material, conducting agent and binder. The specific capacitance of the MnO2 in the MnO2/CNT nanocomposite is as high as 580Fg−1 (320mAhg−1), indicating excellent electrochemical utilization of the MnO2. The addition of CNTs as a conducting agent improves the high-rate capability of the MnO2/CNT nanocomposite considerably. The in situ X-ray absorption near-edge structure (XANES) shows improvement in the structural and electrochemical reversibility of the MnO2/CNT nanocomposite after heat-treatment.