Co3O4/RuO2·xH2O composites with various Ru content (molar content of Ru=5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO3)2·6H2O and RuCl3·0.5H2O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru=1:1 annealed at 200°C, Brunauer–Emmet–Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107m2 g−1. The electrochemical performances of these composites were measured in 1M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642F/g was obtained for the composite (Co:Ru=1:1) annealed at 150°C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM).