A new type of proton conducting fuel cell membrane has been fabricated and evaluated via preliminary physical property determinations. The membrane is composed of a 3-D interconnected network of Nafion (perfluorosulfonic acid) nanofibers that have been embedded in an uncharged and inert polymer matrix. Nafion was successfully electrospun into fibers by adding to the spinning solution a low concentration (1 wt% relative to Nafion) of high molecular weight poly(ethylene oxide). Membranes were made with an average fiber diameter in the range of 161-730 nm, where the nanofiber mat occupied 60-80% of the membrane volume. The inert matrix polymer was UV-crosslinked Norland Optical Adhesive 63. The resulting membranes exhibited a high proton conductivity (0.06-0.08 S/cm at 25°C in water), low water swelling (12-23 wt% at 25°C), and improved mechanical properties, as compared to a recast homogeneous Nafion film.