Nanostructured manganese oxides/exfoliated graphite (MnO2/EG) are prepared using ultrasonic vibration in an aqueous solution. The structures of the MnO2/EG synthesized with different contents of EG are examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) method. The electrochemical performances of composite electrodes are investigated using cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Electrochemical data of the composite electrodes tested in the 0.5 M Na2SO4 solution shows supercapacitive behavior in the voltage window of 0-1.0 V versus Ag/AgCl. At the mass ratio of MnO2/EG of equal to 60:40, the specific capacitance value of the sample calculated from the cyclic voltammetry curves at the scan rate of 2 mV s(-1) is 358 F g(-1) whereas this value for the pure gamma-MnO2 is 289 F g(-1). The specific capacitance of the MnO2/EG at the scan rate 30 mV s(-1) is 240 F g-1, which is decreased to 209 F g-1 after 1000 cycles. The capacitance retention of the composite is 87%. The MnO2/EG composite electrode represents an energy density of 51 W h kg(-1)at a power density of 500W kg(-1), which is much higher than that of pure gamma-MnO2. (C) 2014 Elsevier B.V. All rights reserved.