Carbon nanotube (CNT)/MnO2 composites are synthesized by reduction of potassium permanganate under microwave irradiation. The morphology and microstructure of samples are examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical properties are characterized by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). Birnessite-type MnO2 homogeneously coats on the surfaces of CNTs. For CNT–15%MnO2 composite, the specific capacitance based on MnO2 is 944 (85% of the theoretical capacitance) and 522Fg−1 at 1 and 500mVs−1, respectively. When the content of MnO2 reaches 57wt%, the composites have the maximum power density (45.4kWkg−1, the energy density is 25.2Whkg−1). Therefore, CNT/MnO2 composites prepared by microwave irradiation are promising electrode materials in hybrid vehicle systems.