Ruthenium-embedded carbon nanofibers were prepared by the processes of stabilization, carbonation, and activation after electrospinning a composite solution of ruthenium (III) acetylacetonate and polyacrylonitrile in N, N-dimethylformamide. When Ru particles were embedded in the carbon nanofibers, the average pore diameter increased from 2.0 to 2.5 nm. The Ru particles were embedded randomly within the carbon fibers, and the size distribution of the Ru particles ranged from 2 to 15 nm. The specific capacitance of the carbon nanofiber without the Ru loading was 140 F/g, while that of 7.31 wt % Ru-carbon nanofibers increased to 280% as 391 F/g. This was attributed to the synergistic effect of electric double-layer capacitance as a result of the expansion of the average pore diameter as well as the pseudocapacitance by the well-dispersed Ru particles. (c) 2007 The Electrochemical Society.