Composite membranes have been prepared from perfluorinated ionomer (10 wt % PFSA-H+ solution) and boron phosphate (BPO4). The contents of solid BPO4 in the composite membrane varied from 10 to 50 wt %. The conductivity of the composite membranes measured both at room temperature and at higher temperatures was found to increase with the incorporation of boron phosphate particles into PFSA ionomer. The highest conductivity of 6.2 x 10(-2) S/cm was found for the composite membrane containing 50% BPO4 at 120 degrees C. The membranes were characterized by X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy, which confirmed the presence of solid BPO4 into the membranes. The morphology of the membranes showed the even distribution of BPO4 particles into the composite membranes. These membranes have a strong potential to be considered for use in direct methanol fuel cells. (c) 2005 The Electrochemical Society. All rights reserved.