Solution-cast membranes from perfluorosulfonated ionomers (PFSI) and their blends were prepared from E. I. du Pont de Nemours’s Nafion 117 and Dow Chemical’s experimental membrane XUS. Water sorption and ac impedance measurements were performed on the solution-cast membranes in an attempt to characterize their electrical properties. Water uptake versus relative humidity for the solution-cast membranes was measured and it was observed that the solution-cast membranes imbibe less water than as-received membranes. The dc conductivity was extracted from the impedance measurements, and the room temperature dc conductivity of the solution-cast membranes was found to be approximately 10(-7)-10(-8) S/cm, approximate to 10(4) times lower than the room temperature conductivity of the original PFSI membranes. Impedance analysis also revealed the existence of the gamma-relaxation in the solution-cast membranes. The drastic drop in conductivity and the existence of the gamma-relaxation are thought to be caused by structural changes in the solution-cast PFSI as is supported by high-resolution wide-angle X-ray diffraction (WAXD) measurements.