NiO/sulfonated graphene(NiO/SGN) composites were fabricated under the assistance of urea as supercapacitor materials. The composites as prepared possess the leaf vein-like morphology, forming the porous structure that benefits the enhancement of pseudocapacitive performance. Moreover, the introduction of sulfonated graphene contributes to the surface hydroxylation of NiO, which may increase electrochemically active sites on the surface of NiO. The electrochemical measurements demonstrate that specific capacitances of NiO, NiO/thermally reduced graphene(NiO/TRG) and NiO/SGN are 200, 261 and 307 F g(-1) at a current density of 5.0 A g(-1) respectively, suggesting that the significant improvement of pseudocapacitive performance for NiO/SGN could be expected. The results from electrochemical impedance spectroscopy(EIS) demonstrate that sulfonated graphene can not only provide electron transport channels for its composites similar to thermally reduced graphene, but also benefit the electrolyte penetration in the composites compared with thermally reduced graphene. (C) 2014 Elsevier Ltd. All rights reserved.