MFI type zeolite membranes were synthesized on two types of supporting materials, i.e., alumina and yttria-stabilized zirconia (YSZ) coated alumina. MFI type zeolite membranes without YSZ intermediate layer showed relatively large H2 and He permeance. After repeated secondary growth, the temperature dependency of H2, He, and CO showed little change but the behavior of CO2 was dramatically different. YSZ intermediate layer was quite effective in preventing the aluminum diffusion from alumina support to zeolite layer at high temperatures. A MFI type zeolite membrane with YSZ intermediate layer showed high stability in steam at high temperature. This is an abstract of a paper presented at the 2006 AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).