There are a number of electrochemical and electromechanical applications where it is desirable to electrospin Nafion into nanofibers, including composite fuel cell membranes, sensors, and polymer-based actuators. Nafion and other perfluorosulfonic acid polymers, however, are notoriously difficult to electrospin and require the presence of a high molecular weight carrier polymer in the electrospinning solution. In this paper, we report on the morphology of electrospun Nafion nanofiber mats that are created using a low concentration (1-2 wt %) of poly(ethylene oxide) (PEO) as the carrier polymer. The effects of electrospinning conditions, i.e., air humidity, polymer solution solvent, carrier polymer molecular weight, electrospinning voltage, and electrospinning flow rate, on the quality of the electrospun mat (i.e., the presence/absence of unwanted bead or bead-on-fiber morphologies) and the mat-averaged nanofiber diameter are presented and discussed. Bead-on-fiber structures are more prevalent when Nafion is electrospun at high humidity conditions and when the applied voltage is high. Ribbon-like morphologies form when a high molecular weight PEO carrier polymer is used. Nafion/PEO fiber diameter depends strongly on air humidity, solution solvent, carrier polymer molecular weight, and electrospinning flow rate, where the average diameter of well-formed Nafion/PEO nanofibers can be easily varied from 300 to 900 nm. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3561645] All rights reserved.