Proton conductive inorganic-organic hybrid films, which show high proton conductivity at temperatures higher than 100 degreesC with low relative humidity, were prepared from 3-glycidoxypropyltrimethoxysilane (GPTMS), tetramethoxysilane (TMOS) and orthophosphoric acid by the sol-gel method. The relative humidity dependence of the conductivity measurements showed that the ionic conductivity of the films, which increased with an increase in the relative humidity, was about 5 x 10(-2) S cm(-1) under 20% relative humidity (RH) at 130 degreesC. The polarization performances measured for test cells at 130 degreesC showed that the maximum power density increased with an increase in the relative humidity. For a cell with the hybrid film (molar ratio P/Si = 1.5) as an electrolyte under H-2 and air at 130 degreesC, 17% RH, the open circuit voltage of the cell was about 0.88 V and a power of about 50 MW cm(-2) was obtained with current density of 150 mA cm(-2) (C) 2004 Elsevier Ltd. All rights reserved.