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 (3–5nm in size) on graphene sheets. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 243.2Fg−1 has been obtained at a scan rate of 10mVs−1 in 6M KOH aqueous solution for GNS/Co3O4 composite. Furthermore, the composite exhibits excellent long cycle life along with ∼95.6% specific capacitance retained after 2000 cycle tests.