We report a simple and convenient method for the synthesis of functionalized graphene nanosheets/carbon nanotubes networks (G/CNTs-200) through chemical oxidation followed by low temperature treatment reduction. The G/CNTs-200 sample has the unique hybrid structure consisting of 1D carbon nanotubes as the continuous conductive networks and 2D functionalized graphene nanosheets as pseudocapacitive materials. Significantly, such unique hybrid structure ensures high surface area and suitable oxygen functional groups without obviously sacrificial conductivity. As a result, the G/CNTs-200 electrode exhibits a specific capacitance of 202 F g(-1) at a current density of 0.5 A g(-1), which is almost five times higher than that of pure CNTs (40 F g(-1)). Interestingly, it can keep a high capacitance retention ratio of 60% at a current density of 50 A g(-1) in 6 mol L-1 KOH aqueous electrolyte. More importantly, a symmetric device based on G/CNTs-200 electrodes delivers an energy density of 11.7 W h kg(-1) and excellent electrochemical stability in 1 mol L-1 Na2SO4 aqueous electrolyte. Therefore, this work holds a great promise for the design and large-scale production of CNTs-based electrode materials for high performance supercapacitors.