In order to estimate the durability of Nafion((R)) membrane as an electrolyte for direct methanol fuel cells (DMFCs), the degree of dissolution of Nafion((R)) membranes in mixtures of methanol and water at various temperatures up to 80degreesC was examined. At 80degreesC, more than 30% of the membrane was dissolved in mixed solvents with methanol concentrations of higher than 80%. Dissolution of recast films made from Nafion((R)) solution was also examined, because it is an important component of the catalyst layers of DMFCs. The effects of heat treatment on the durability of the recast films were also examined. Although high temperature (160 degreesC for 1 min) or long time (120 degreesC for 1 h) heat treatment improved significantly the durability at room temperature, the films were dissolved at 80 degreesC and the amounts of dissolution were larger than that of Nafion((R)) 117 membranes. (C) 2003 Elsevier B.V. All rights reserved.