The arc-soot (AS) nano-carbon was synthesized by using arc discharge apparatuses which were the conventional arc apparatus and the new twin-torch-arc apparatus. AS synthesized with the conventional arc apparatus contained cocoon-like carbon nano-horn (CNH), dahlia-like CNH, and graphite ball. On the other hand, AS which was synthesized using the new twin-torch-arc apparatus contained mainly cocoon-like CNH and dahlia-like CNH, and contained a little graphite ball. The quality of dispersion was characterized and evaluated by the index of dispersion which was based on a diameter and a number density of catalyst particles. The electrocatalystic activity of the Pt/Ru catalysts was evaluated by the methanol-impregnated paper burning method. If the index of dispersion of the AS was high, then the AS burned violently. In the dispersion process, the optimum dispersion temperature obtained was 150 degrees C. Some MEAs of DMFC cell consisted of each Pt/Ru-AS catalyst which had different characteristics. It was observed that the power density increased with the index of dispersion. It was suggested that the power density of DMFC increased by 500% with a 350% increase in the index of dispersion. Pt/Ru-AS catalyst used AS, which was synthesized using the new twin-torch-arc apparatus, was better than Pt/Ru-AS catalysts using AS which were synthesized with the conventional arc apparatus to apply for the catalyst of DMFC. (C) 2008 Elsevier B.V. All rights reserved.