Nafion 117 membranes were modified by in situ chemical polymerization of 3,4-ethylenedioxythiophene using H2O2 as oxidant for direct methanol fuel cell application. Methanol permeability and proton conductivity of the poly(3,4-ethylenedioxythiophene)-modified Nafion membranes as a function of temperature were investigated. An Arrhenius-type dependency of methanol permeability and proton conductivity on temperature exists for all the modified membranes. Compared with Nation 117 membrane at 60 degrees C, the methanol permeability of these modified membranes is reduced from 30% to 72%, while the proton conductivity is decreased from 4% to 58%, respectively. Because of low methanol permeability and adequate proton conductivity, the DMFC performances of these modified membranes were better than that of Nation 117 membrane. A maximum power density of 48.4 mW cm(-2) was obtained for the modified membrane, while under same condition Nafion 117 membrane got 37 mW cm-2. (C) 2007 Elsevier B.V. All rights reserved.