Nanosized hydrous RuO2/Ketjen Black (KB) composites were prepared using an in situ sol-gel process induced by ultracentrifugal mechanical force for supercapacitors. The hydrous RuO2 in the prepared samples were nanosized particles ca. 2 nm and were highly dispersed on conductive carbon (KB) even at high hydrous RuO2 content (50 wt %). The composite annealed at 150 degrees C exhibited the high specific capacitance of 821 F g(-1), which corresponds to a charge utilization as high as 96%. Such a high charge utilization could be because the nanoparticles have both outer and inner hydrous channels which facilitate ionic transport. A model capacitor assembled using the composite exhibited energy and power densities as high as 12 Wh kg(-1) and 6 kW kg(-1), respectively.