Silica　membranes　modified　with　phenyl　groups　were　synthesized　through　the　acid-catalyzed　co-hydrolysis　and　condensation　reaction　of　tetraethyl　orthosilicate　(TEOS)　and　phenyltriethoxysilane　(PTES)　The　pore　structure　and　hydrophobic　properties　of　the　modified　silica　membranes　were　characterized　by　means　of　SEM,　nitrogen　adsorption,　water　contact　angle　measurement,　TG　and　FTIR.　The　single　gas　permeation　and　permselectivity　of　the　hydrophobic　silica　membranes　were　also　investigated　at　room　temperature:　The　results　show　that　the　hydrophobic　properties　of　the　modified　silica　membranes　are　gradually　enhanced　with　increasing　amount　of　PTES　in　the　mixture.　When　the　molar　ratio　of　PTES/TEOS　increases　to　0.6　and　the　molar　ratio　of　H2O/TEOS　to　9.6,　the　modified　silica　membranes　exhibit　an　excellent　hydrophobic　property　with　a　water　contact　angle　of　115　degrees　+/-　0.5　degrees　and　a　desirable　microporous　structure　with　4　pore　volume　of　0.17　cm(3)/g　and　a　sharp　pore　size　distribution　centered　at　0.4-0.5　nm.　The　modified　silica　membranes　conform　to　a　combination　of　a　surface　diffusion　mechanism　associated　with　micropores　and　a　Knudsen　diffusion　mechanism　related　to　the　larger　pores　or　microcracks,　with　a　H-2　permeance　of　1.49　x　10(-6)　mol/(m(2).Pa.s)　and　a　permselectivity　of　4.64　for　H-2/CO3　and　365.69　for　H-2/SF6.