Highly structurally controllable mesoporous carbon (MC) support was synthesized through the self-organization of surfactants and carbon precursors, followed by carbonization. Then, Pt catalysts were successfully deposited on MC, in order to create a model of an ideal triple phase boundary in such a nano-space. The resulting Pt/MC catalysts showed better oxygen reduction reactivity with the existence of Nafion (R) than without that. Handling of ionomers is a key to develop an ideal triple phase boundary within the pores of MC. Depending on the solvent where Nafion (R) was diluted, the reactivity toward oxygen reduction was different. Due to its hydrophobic pores of MC, Nation (R) diluted by more hydrophobic solvent was able to access to the pores easily. As a result, Pt inside the mesopores was efficiently used. Furthermore, by changing a Pt precursor, oxygen reduction current started to increase at more positive potential, indicating the enhanced activity. (C) 2008 Elsevier Ltd. All rights reserved.