A series of cobalt oxide/graphene nanocomposites have been successfully synthesized by adding carbon blacks filler. We have introduced carbon blacks to act as a structural modifier in fabricating graphene based composites. The composites were prepared by ultrasonication and microwave-assisted methods. Microstructure measurements showed that carbon blacks could be conductive links among layers of graphene and cobalt oxide particles (5-7 nm in size), which was deposited on the edge surfaces of nanosheets. This composite could function as a stable structured blocks for preventing an aggolomeration of graphene layers. The electrochemical properties are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). The prepared nanocomposites showed the superior capacitive performance with good rate capability, large specific capacitance, and excellent cyclic performance. Among various samples, Co3O4/GNS-CB (15 wt.%) showed the largest specific capacitance of 341 F g(-1) at a scan rate of 10 mV s(-1) in 6 M KOH electrolyte. Therefore, the prepared composite could be potential electrode materials for supercapacitors. (C) 2012 Elsevier Ltd. All rights reserved.