The phosphosilicate sol/sulfonated poly(ether ether ketone) (SPEEK) composite membranes are fabricated by using a simple mechanical mixing process. The performance of the composite membranes is investigated, including their morphology, thermal and mechanical properties, water adsorption and swelling ratio, proton conductivity and fuel cell performance. The composite membranes obtain the advantages of both components while avert their disadvantages, showing excellent comprehensive performance. The utilization of SPEEK endows the composite membranes with good mechanical properties even if the proportion of inorganic components in the membranes is as high as 40 wt.%. The incorporation of phosphosilicate sol not only enhances the dimensional and thermal stability of the composite membranes, but also improves their conductivity significantly. A maximum of proton conductivity of 0.138 S cm(-1), higher than that of Nafion 212 membrane (0.124 S cm(-1)), is obtained from the composite membrane 6SPEEK/4(P-Si) under the conditions of 70 degrees C and 95% relative humidity, owing to its enhanced hygroscopicity and functional groups. Besides, a single fuel cell equipped with the composite membrane 7SPEEK/3(P-Si) releases a peak power density of 449.9 mW cm(-2) at 60 degrees C, higher than that of cells equipped with SPEEK and Nafion 212 membrane measured under the same conditions. (C) 2015 Elsevier B.V. All rights reserved.