Mesoporous NiO/reduced graphene oxide composites are successfully synthesized by a facile hydrothermal route. The XRD, FT-IR, Raman, SEM, TEM, and BET analysis are performed for characterizing the microstructure of the as-prepared composites. It can be found that the NiO particles with mesoporous structure are randomly anchored onto the surface of graphene sheets. The electrochemical performance is evaluated by CV, EIS and galvanostatic charge-discharge tests. Experimental data show that the NiO/RGO composites exhibit very high specific capacitance (1016.6Fg−1) and excellent cycling stability (94.9% capacitance retention after 5000 cycles), which are due to the 3D graphene conductive network and the meosporous structure promoting efficient charge transport and electrolyte diffusion. The results suggest that the NiO/RGO composites are a promising supercapacitor electrode material.