Proton conductive inorganic -organic hybrid films, which show high proton conductivity at temperatures higher than 100 degrees C with low humidification, have been prepared from epoxycyclohexylethyltiimethoxysilane (EHTMS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and H3PO4 by the sol-gel method. Self-supporting, flexible films with a thickness of about 150 to 300 pm were obtained. The ionic conductivity of the films increased with an increase in the relative humidity and was about 1 X 10(-2) S cm(-1) under 25% relative humidity at 130 degrees C. For a fuel cell with the hybrid film (P/Si= 1.5) as an electrolyte under H-2 and air at 130 degrees C, 17% relative humidity, the open circuit voltage of the cell was about 2 2 0.9 V and a power of about 40 mW cm(-2) was obtained with current density of 110 mA cm(-2). It was also confirmed that the test cell can operate 2 more than 10 h with a current density of 100 mA cm(-2). (c) 2005 Elsevier B.V. All rights reserved.