In this work, a gas diffusion electrode (GDE) with a catalyst layer containing a mixture of Nafion and polyaniline (PANI) nonofiber was prepared by a simple method. The resulting GDE had good mechanical properties and acceptable electrochemical activity. This type of modified electrode could potentially be applied in the development of membrane-electrode assembly. The surface morphologies of the Nafion-PANI-modified GDE and the corresponding GDE modified with Nafion alone were characterized by scanning electron microscopy. The electrochemical properties of the electrodes were characterized using cyclic voltammetry, I-V polarization curves, AC impedance spectroscopy and chronoamperometry. The results indicated that, compared to the electrode with Nation alone, the electrode containing PANI nonofiber in the catalyst layer had higher catalyst utilization for the oxygen reduction reaction. The improvement in electrode performance on introduction of PANI can be related to the increasing of good electronic conductance between aglomerations in parallel to ionic conductivity in the reaction layer due to the presence of homogenously dispersed PANI nanofibular and Nafion. (c) 2005 Elsevier B.V. All rights reserved.