Reduced graphene oxide (RGO)/nickel cobaltite (NiCo2O4) nanoflake composites were prepared by combining in situ assembling and subsequent thermal treatment. The RGO/NiCo2O4 composites were characterized by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption/desorption isotherms and thermogravimetric analysis. Cyclic voltammetry and chronopotentiometry measurements were performed to investigate the electrochemical properties of the composites. Superior performances were achieved with high specific capacitance of 1693Fg−1 at 1Ag−1, good rate capability (67.6% capacity retention at 16Ag−1) and long-term cyclability (only 9.2% loss after 2000 cycles). The binary redox couples of Ni2+/Ni3+ and Co2+/Co3+, ultrathin nanoflake structure, together with the high electrical conductivity of RGO to the outside current collectors are responsible for the excellent electrochemical performances of the RGO/NiCo2O4 composite, thus suggesting its potential application as an effective electrode material for supercapacitors.