gamma-Al2O3　membranes　were　successfully　deposited　on　the　top　of　porous　alpha-Al2O3　support　by　sol-gel　process　and　characterized　by　means　of　XRD,　SEM,　N-2　adsorption　and　gas　permeation.　The　gamma-Al2O3　membranes,　free　of　pin-holes　and　cracks,　adhere　tightly　to　the　supports　and　have　a　thickness　of　about　7　mu　m.　When　sintered　at　400　degrees　C,　gamma-Al2O3　membranes　have　a　narrow　pore　size　distribution,　with　a　pore　diameter　of　3.6nm,　and　the　transport　of　both　H-2　and　CO2　in　supported　gamma-Al2O3　membrane　is　governed　by　Knudsen　mechanism,　with　H-2　permeance　of　3.3　x　10(-1)　molm(-2)　Pa-1　s(-1)　and　H-2/CO2　permselectivity　close　to　the　ideal　Knudsen　value　at　50　degrees　C.　The　gamma-Al2O3　membranes　are　suitable　for　being　used　as　the　substrates　of　microporous　membranes.