electrode assemblies with Nafion/nanosize titanium silicon dioxide (TiSiO4) composite membranes were manufactured with a novel ultrasonic-spray technique and tested in proton exchange membrane fuel cell (PEMFC). Nafion/TiO2 and Nafion/SiO2 nanocomposite membranes were also fabricated by the same technique and their characteristics and performances in PEMFC were compared with Nafion/TiSiO4 mixed oxide membrane. The composite membranes have been characterized by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, water uptake, and proton conductivity. The composite membranes gained good thermal resistance with insertion of inorganic oxides. Uniform and homogeneous distribution of inorganic oxides enhanced crystalline character of these membranes. Gas diffusion electrodes (GDE) were fabricated Ultrasonic Coating Technique. Catalyst loading was 0.4 mg Pt/cm(2) for both anode and cathode sides. Fuel cell performances of Nafion/TiSiO4 composite membrane were better than that of other membranes. The power density obtained at 0.5 V at 75 degrees C was 0.456 W cm(-2), 0.547 W cm(-2), 0.477 W cm(-2) and 0.803 W cm(-2) for Nafion, Nafion/TiO2, Nafion/SiO2, and Nafion/TiSiO4 composite membranes, respectively. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.