Mesoporous gamma-Al2O3-based membranes, namely gamma-Al2O3 alone, La2O3-doped Al2O3, Ga2O3-doped Al2O3 and La2O3-doped Ga2O3-Al2O3, were prepared by the sol-gel method to test their stability in hydrothermal conditions at 500 degreesC. The hydrothermal (up to 75% steam) stability, of all fabricated membranes formed on an alpha-Al2O3 porous Support through dip coating process was characterized by HI gas permeation. The H-2, gas permeance was drastically increased in 2 h under hydrothermal conditions for all samples except La2O3-doped Ga2O3-Al2O3. Steady-state gas permeance performance and unchanged morphology as well as pore size before and after hydrothermal test revealed that the La2O3-doped Ga2O3-Al2O3 membrane in the composition of La:Ga:Al =6:30:64 mol% with gamma-Al2O3 phase structure could be withstand during prolonged exposure to high temperature (500 degreesC), especially in the presence of steam. The hydrothermal test indicates that the membrane prepared is viable to be of use as an intermediate layer for fabricating a microporous gas separation membrane. (C) 2004 Elsevier B.V. All rights reserved.