A novel ternary composite membrane is prepared by inverse phase separation of a mixture containing silyl functionalized poly(vinylidene fluoride) (SF-PVDF), phosphotungstic acid (PWA) and 3-aminopropyltrimethoxysilane (APTMS). The composition and structure of the resulting membranes are characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and a Universal Testing Machine (UTM). Water uptake and PWA loss of the membrane are examined for different membrane types as well as PWA amounts in the membranes. The effect of membrane type, temperature and the amounts of PWA on proton conductivity are also studied. It is found that the loss of PWA and water contained in the membrane dramatically decreases by adding suitable amounts of APTMS to the membranes. The novel ternary composite membrane, with good mechanical strength and thermal stability, can reach a proton conductivity of 0.01 S cm(-1) under moderate conditions. (c) 2009 Elsevier B.V. All rights reserved.