DuPont's Nafion^® perfluorosulfonic acid cation-exchange membranes possess many desirable properties for PEM fuel cells which operate at a temperature £ 80°C, including high proton conductivity under fully hydrated conditions and good thermal and oxidative stability. Unfortunately, methanol crossover in these membranes is unacceptably high when they are used in a direct methanol fuel cell (DMFC) and the mechanical properties of Nafion under humidity cycling in a hydrogen/oxygen fuel cell are less than satisfactory. A new Nafion membrane fabrication method has been developed, with a new and permanent membrane micromorphology, where a solution cast film is uniaxially stretched and then annealed. Uniaxial stretching of recast Nafion up to a draw ratio of four had no effect on proton conductivity (0.1 S/cm at 25°C for membranes in water), but it did lower methanol permeability by a factor of 1.4-2.0. A pre-stretched recast Nafion film in the 130-180 µm thickness range (draw ratio of 4), when used in a direct methanol fuel cell (DMFC), generated a high power density at 0.4 V (88 mW/cm² at 60°C, 1.0 M methanol, and ambient pressure air), as compared to 58 mW/cm² for Nafion 117. Membrane-electrode assemblies (MEAs) with pre-stretched recast Nafion consistently out-performed Nafion 117 in a DMFC at methanol feed concentrations in the range of 0.50-10.0 M, with 33-48% higher power densities at 0.4 V, due to a combination of low membrane area-specific resistance (the use of a thinner pre-stretched membrane, where the conductivity was the same as that for commercial Nafion) and low methanol crossover (due to low methanol solubility in the membrane). Equilibrium water sorption, differential scanning calorimetry, electro-osmotic drag coefficient, and pulsed field gradient NMR diffusion coefficient analyses of water in pre-stretched recast Nafion revealed that: (1) the total water content in the pre-stretched films was the same as that in commercial Nafion, (2) there was less free/freezable water in pre-stretched films, and (3) the water self diffusion coefficient was the same in Nafion 117 and pre-stretched recast Nafion, and (4) the electro-osmotic drag coefficient was smaller after Nafion elongation. The experimental data suggested that there were a greater number of small water-filled domains in pre-stretched Nafion, as compared to commercial Nafion (this morphology was confirmed by TEM images of membrane cross sections). Pre-stretched recast Nafion also exhibited properties that are desirable for hydrogen/oxygen fuel cell applications. The proton conductivity of water-equilibrated pre-stretched Nafion films at T=–20°C was 30-50% higher than that of commercial Nafion (conductivity under freezing conditions is important for cold weather fuel cell operation) and the mechanical properties were improved (the films were stronger), as quantified by a high ultimate tensile strength and high storage modulus (the improvement in mechanical properties was associated with an increase in polymer crystallinity upon stretching).