Abstract: A reduced graphene/carbon black composite was prepared by reducing homogeneous mixed suspensions of graphene oxide and carbon black oxide with hydrothermal method. The structure and electrochemical performance of the composite were characterized by the techniques of X-ray diffraction and field emission scanning electron microscope, cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The results show that the nano-sized carbon black particles are successfully intercalated into graphene nanosheets, the agglomeration of graphene nanosheets is effectively restrained, the graphene layer spacing increases, and a composite with open 3-D channel structure is formed. The specific capacitance and rate capability of the composite are obviously better than those of the pristine graphene.