Graphene nanosheet (GNS)/Co3O4 composite has been rapidly synthesized by microwave-assisted method. Field emission scanning electron microscopy and transmission electron microscopy observation reveals the homogeneous distribution of Co3O4 nanoparticles (3-5 rim in size) on graphene sheets. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 243.2 g(-1) has been obtained at a scan rate of 10 mV s(-1) in 6 M KOH aqueous solution for GNS/Co3O4 composite. Furthermore, the composite exhibits excellent long cycle life along with similar to 95.6% specific capacitance retained after 2000 cycle tests. (C) 2010 Elsevier Ltd. All rights reserved.