In this paper, the optimum Nafion ionomer content in platinum (Pt) dispersed on ordered mesoporous carbon (OMC) catalyst is investigated. The ionomer content can affect catalytic activity, ionic conductivity and mass transfer characteristics. A nano-replication method using ordered mesoporous silicas (OMS) is applied to prepare OMCs, and Pt/OMC with high loading are synthesized by the incipient wetness method for polymer electrolyte membrane fuel cells (PEMFCs). Catalyst characteristics have been analyzed using TGA, XRD, TEM and BET. Cathode electrodes have different ionomer loadings (in the range of 5-30 wt. %) with Pt/OMCs. Commercial Pt/C catalyst is used in anode. All membrane electrode assemblies (MEAs) fabricated by the decal transfer method show about 0.4 mg cm(-2) Pt loading. The PEMFC performances have been measured by electrochemical methods such as polarization curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The performances is different at low and high current density regions, and the optimum content of ionomer is 10 wt. % in the catalyst, due to unique structure of OMCs. (C) 2012 Elsevier B.V. All rights reserved.