Three dimensional (3D) porous graphene decorated with MoO2 nanoparticles were successfully synthesized by hydrothermal method and characterized by SEM and TEM, x-ray diffraction, Raman spectra, x-ray photoelectron spectroscopy, nitrogen adsorption–desorption analysis and electrochemical experiments. The results revealed that the in situ formed monoclinic MoO2 nanoparticles were randomly decorated on the surface of graphene sheets and the obtained graphene–MoO2 nanohybrids were 3D porous structures. The mass ratio of molybdenum precursor with GO has effects on the specific surface area and the electrochemical properties of the nanocomposite. The M30G1 (the mass ratio of molybdenum precursor with GO was 30:1) composite electrode exhibited a higher specific capacitance and better cycling stability. The specific capacitances were 356 F/g at the current density of 0.1 A/g in KOH electrolyte, which predicted their potential application in energy storage. The electrochemical performance of M30G1 composite was also investigated in Na2SO4 electrolyte, which was poorer than that in KOH electrolyte. Therefore, the chosen of electrolyte is important to materials performance.