High proton conducting Nafion/calcium hydroxyphosphate (CHP) composite membranes were prepared through homogeneous dispersive mixing and solvent casting method for fuel cell applications. The fabricated membranes were characterized by wide-angle X-ray diffraction (WAXD), Fourier-transform infrared spectrum (FT-IR), and focused ion beam (FIB). The crystallinity calculated by Gaussian peak deconvolution technique increases as the CHP increases in composite membranes. It is likely that the incorporated CHP fine particle forms a new crystalline area in the amorphous region or even crystalline region, which means the CHP plays a role in a kind of nucleating agent for Nation. In the FT-IR study, it was found that the absorbance of OH- bending peak at 1673 cm(-1) decreases as the number of scan increases. In the FIB pictures, three-dimensional holes or channels were shown. In the study of proton conductivity, that of composite membrane is higher than that in cast Nafion. Consequently, we may conclude that the incorporated CHP particles influence the crystalline kinetics and structure modification for cast Nafion, resulting in the increase of conductivity in Nafion/CHP composite membranes. (C) 2004 Elsevier Ltd. All rights reserved.