The importance of developing high-performance electrode materials with low cost for supercapacitors is self-evident. In this paper, composites of KOH activated carbon/graphene nanosheets were prepared via a simple hydrothermal treatment of graphite oxide and KOH activated carbon. The electrochemical experiments that were conducted demonstrate that these composites exhibited synergistically improved electrochemical performance as electrodes in a supercapacitor. The specific capacitance of these composites can reach as high as 205 and 173 F g⁻¹ in 6 M KOH aqueous solution and 1 M TEABF₄ in acetonitrile solution, respectively. In addition, the as fabricated electrodes that were obtained using these composites show a reduced internal resistance and higher capacitance retention performance. Furthermore, the entire preparation process is simple, low cost and easily scalable to mass production, leading to great potential application in supercapacitors for as prepared composites.