Abstract Proton-conducting composite membranes were prepared by doping phosphosilicate gels into SPPO polymer matrix. The structure of gels was examined by 31 P MAS-NMR. The composite membranes were characterized in terms of TGA, mechanical property, water uptake and conductivity. It was found that the composite membranes were thermally stable up to 150 °C, and possessed higher mechanical strength than Nafion112, either in dry state or in wet state. The conductivity of composite membranes increased with the increase of the ion exchange capacity (IEC), relative humidity (R.H.) and doping amounts. The water uptakes of composite membranes are much higher than Nafion112 in weight percent form at room temperature, and the highest conductivity value of 0.216 S cm − 1 was achieved for water equilibrated membranes, 2.5 times higher than 0.0871 S·cm − 1 for Nafion112 measured under the same condition. It is suggested that the composite membranes should be the promising candidates used in PEMFC.