An easy and efficient method to reduce graphene oxide (GO) with manganese powder under mildly acidic conditions with ultrasonication for 30 min at room temperature has been developed. The reduction process was traced by UV-visible absorption spectroscopy, and the obtained reduced graphene was characterized by X-ray diffraction (XRD), Raman microscope, thermo-gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results showed that Mn powder is an efficient reducing agent for the reduction of GO. The Mn2+ ions produced during the redox reaction between GO and the manganese powder were chemically transformed to MnO2 and then formed MnO2/RGO composites. The MnO2/RGO composites were used as electrode materials and their capacitance was studied by cyclic voltammetry and galvanostatic charge/discharge. The MnO2/RGO composites showed excellent electrochemical performance with a highest specific capacitance of about 330 F.g(-1). (C) 2014 Elsevier Ltd. All rights reserved.