We report methanol permeability and ionic conductivity of a Nafion 117 film doped with 1-ethyl-3-methylimidazolium cation (EMI+). Methanol permeability is 2.83 x 10(-7) cm(2)/s at room temperature in this film, compared to 30.8 x 10(-7) cm(2)/s in an undoped Nafion film, and exhibits an Arrhenius dependence upon temperature. Ionic conductivity for EMI+-doped Nation is 0.0326 S/cm, compared with 0.0872 S/cm for undoped Nafion. A high ratio of ionic conductivity to methanol permeability signals a membrane with desirable properties, and the EMI+-doped membrane has a ratio of 9.797 x 10(4) S cm/s. The log of this ratio is linear with increasing temperature. All values are comparable to those in the literature. This behavior is explained by EMI+'s decreasing the mobility of water molecules within Nafion and the resulting loss in methanol mobility within those water pools. (C) 2004 The Electrochemical Society.