Methyl-modified　mesoporous　silica　membranes　were　prepared　by　acid　catalyzed　co-hydrolysis　and　condensation　reaction　of　tetraethylorthosilicate　(TEOS)　and　methyltriethoxysilane　(MTES)　in　the　presence　of　triblock　copolymer　poly　(ethylene　glycol)-B-poly　(propylene　glycol)-B-poly　(ethylene　glycol)　(P123)　in　ethanol.　The　pore　structure　and　hydrophobic　property　of　the　final　materials　were　characterized　by　Nitrogen　adsorption,　FTIR,　Si-29　MAS　NMR　and　contact　angle　meter.　The　results　show　that　modified　silica　membranes　have　a　desirable　pore　structure,　with　a　pore　size　of　4.65　nm,　a　pore　volume　of　0.69　CM3.g(-1)　and　a　BET　surface　area　of　938.4　m(2).g(-1),　and　tend　to　be　hydrophobic　with　a　water　contact　angle　of　109　degrees　+/-　1.1　degrees,　as　the　molar　ratio　of　MTES/TEOS　increases　to　1.0.　Gas　permeability　test　suggests　that　the　gas　transport　into　the　membranes　is　governed　by　Knudsen　diffusion　mechanism.