Commercial Nafion 115 membranes were successfully modified by in situ acid-catalyzed polymerization of furfuryl alcohol (PFA) within Nafion structures. FT-IR and AFM were used to characterize the chemical and morphological structures of the Nafion-PFA nanocomposite membrane obtained. The methanol permeation experiments showed that the methanol flux through the Nafion-PFA nanocomposite membranes dropped by a factor of 2.2-2.7 when PFA loading was 3.9-8.0 wt.%. Importantly, the proton conductivity of the membranes decreased only slightly at a low PFA loading (<8 wt.%). The nanocomposite membranes with higher selectivity (e.g., proton conductivity/methanol crossover) achieved a much higher DMFC performance at both room temperature and 60degreesC. (C) 2004 Elsevier B.V. All rights reserved.