The effects of annealing time and humidity on fuel-cell performance and characteristics of solution cast Nafion membranes were investigated experimentally. Membranes cast from commercial Nafion dispersion were annealed at 120 degrees C for 10, 30 or 60 min in a dry or humid oven. Membrane electrode assemblies were made by applying a catalyst layer on cast and commercial membranes. Crystallinity, cell performance, membrane resistance, electrochemical active area, H-2 crossover current and ultimate tensile strength were measured. It has been found that all solution cast membranes perform similarly to the commercial membrane in fuel cells, except the membrane annealed for 10 min in the humid condition, which exhibited slightly worse performance at voltages below 0.6 V. X-ray diffraction (XRD) patterns of cast membranes annealed under dry conditions were found to be similar to commercial membrane; while XRD patterns for cast membranes annealed under humid conditions were found to be similar to un-annealed membrane. From tensile tests, it has been found that cast membranes annealed longer than 30 min in the dry condition have the similar strength as the commercial membrane. (C) 2013 The Electrochemical Society. All rights reserved.