Methyl-modified　silica　membranes　were　prepared　by　acid　catalysed　co-hydrolysis　and　condensation　reaction　of　tetra-ethylortho-silicate(TEOS)　and　methyl-tri-ethoxy-silane(MTES)　in　ethanol　and　characterized　by　TGA,FTIR　and　gas　permeation.　The　hydrophobicity　of　modified　silica　membranes　increases　with　MTES/TEOS　molar　ratio　and　almost　no　water　can　be　adsorbed　on　the　surface　of　the　membranes　with　MTES/TEOS　molar　ratio.　higher　than　0.8.　For　the　modified　silica　membranes　with　METS/TEOS　molar　ratio　of　1,　the　hydrogen　transport　is　activated　by　temperature　with　a　H-2　flux　of　6.0　x　10(-7)　mol(.)m(-2.)Pa(-1.)s(-1)　and　H-2/CO2　separation　factor　of　6.0　at　200degreesC,　and　the　hydrogen　permeance　shows　little　change　and　the　H-2/CO2　separation　factor　increases　after　aging　at　200degreesC　and　a　water　vapor　pressure　of　3564Pa　for　110　hours.　It＇s　shown　that　CH3-modified　silica　membranes　are　more　hydrothermally　stable　than　the　unmodified　silica　membranes.