Effects of methanol, ethanol, 2-propanol and water on the proton conductivity and surface properties of Nafion membrane have been studied by electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). It was established that both conductivity and surface topography decrease in alcohol environment while they show high values and big roughness when Nafion is in aqueous environment. We have measured the conductivity of Nation in water-alcohol mixtures environments and results give evidence of conductivity and dielectric constant dependence, which has been explained on the basis of Born and Arrhenius equations. Nation's surface properties were investigated by contact and tapping AFM modes. Surface topography considerably changes when samples absorb water. However, samples stored in alcohols are characterized by flat surfaces. Surface modification was linked to an expansion phenomenon during the swelling of Nation by solvents. Tapping mode phase images showed that ionic and cluster domains are distinguishable from the surface of samples impregnated either in water or alcohols. (c) 2005 Elsevier B.V. All rights reserved.