Hydrothermally reduced graphene/MnO2 (HRG/MnO2) composites were synthesized by dipping HRG into the mixed aqueous solution of 0.1M KMnO4 and 0.1M K2SO4 for different periods of time at room temperature. The morphology and microstructure of the as-prepared composites were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman microscope, and X-ray photoelectron spectroscopy. The characterizations indicate that MnO2 successfully deposited on HRG surfaces and the morphology of the HRG/MnO2 shows a three-dimensional porous structure with MnO2 homogenously distributing on the HRG surfaces. Capacitive properties of the synthesized composite electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 1M Na2SO4 aqueous solution as electrolyte. The main results of electrochemical tests are drawn as follows: the specific capacitance value of HRG/MnO2–200 (HRG dipped into the mixed solution of 0.1M KMnO4 and 0.1MK2SO4 for 200min) electrode reached 211.5Fg−1 at a potential scan rate of 2mVs−1; moreover, this electrode shows a good cyclic stability and capacity retention. It is anticipated that the synthesized HRG/MnO2 composites will find promising applications in supercapacitors and other devices in virtue of their outstanding characters of good cycle stability, low cost and environmentally benign nature.