A series of cobalt nanoparticles/reduced graphene oxide (Co/RGO) composites have been successfully synthesized via a facile microwave-assisted synthetic route for the first time. The synthesized composites are comprised of Co particles that are uniformly anchored onto the surface of graphene sheets by in situ reducing. Powder X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and Brunauer-Emmett-Teller (BET) analysis are performed for systematically characterizing the microstructure and composition of the as-prepared Co/RGO composites. Interestingly, the as-prepared composites show superior electrochemical performance to their counterparts of Co and RGO as electrodes for supercapacitors. As a result, Co/RGO-15 composite exhibits a high specific capacitance of 370.7 F g(-1) at 5 mV s(-1) in 2 M KOH aqueous solution as well as good rate capability. The excellent electrochemical performances are due to the 3D graphene conductive network and the synergetic effect of RGO and Co particles. Meanwhile, the capacitance retention keeps about 92.3% of the initial value after 2000 cycles at a current density of 2 A g(-1), suggesting that such hybrid electrode possesses a great potential application in energy-storage devices. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.