A facile and cost-effective way has been developed to fabricate a unique structure of Ni3S2 and Co9S8 double-size nanoparticles decorated on rGO (coated on the surface of nickel foam (NF)) and the as-prepared rGO/Ni3S2/Co9S8 composite was directly applied as the electrode for a high-performance supercapacitor. In the absence of rGO, Co-doping Ni3S2 nanoparticles (Co-Ni3S2) were produced. Detailed electrochemical measurements showed that the rGO/Ni3S2/Co9S8 composite electrode exhibited high specific capacitance of 1929.1Fg−1 compared to that of Co-Ni3S2 electrode of 1075.5Fg−1 at a current density of 1Ag−1. In addition, the rGO/Ni3S2/Co9S8 composite displayed excellent rate capability (1669.2Fg−1 at 20Ag−1) and good cycling ability (92.8% capacitance retention after 1000 cycles at a current density of 10Ag−1). The enhanced electrochemical performances of rGO/Ni3S2/Co9S8 composite can be mainly attributed to the positive synergic effect of the unique structure. The facile, low-cost and novel synthesis method and outstanding performance make the rGO/Ni3S2/Co9S8 composite an ideal electrode material for the electrochemical energy storage devices.