We report the simple one-step synthesis of a reduced graphene oxide-manganese oxide (rGO-MnO2) nanocomposite using graphene oxide (GO) and KMnO4 in the presence of sulfuric acid. The crystal structure, morphology, thermal, pore size, and other physical properties of the rGO-MnO2 nanocomposite were systematically analyzed by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller analysis. XPS analysis confirmed the synthesis of exfoliated GO and rGO-MnO2 nanocomposite. The rGO-MnO2 nanocomposite exhibited a maximum specific capacitance, energy, and power density of 290 F g(-1), 25.7 Wh kg(-1), and 8008.7 W kg(-1), respectively, in a 1M Na2SO4 electrolyte, and a high retention (87.5%) of capacitance after 5000 cycles. The enhanced electrochemical properties are caused by good contact between MnO2 nanorods and graphene nanosheets, and the higher conductive and capacitive behavior of graphene. (C) 2017 Published by Elsevier Ltd.