A promising candidate material for a H2 permeable membrane is SiC due to its many unique properties. Ahydrogen-selective SiC membrane was successfully fabricated on the outer surface of an intermediate multilayer γ-Al2O3 witha graded structure. The γ-Al2O3 multilayer was formed on top of a macroporous α-Al2O3 support by consecutively dipping intoa set of successive solutions containing boehmite sols of different particle sizes and then calcining. The boehmite sols wereprepared from an aluminum isopropoxide precursor and heated to 80oC with high speed stirring for 24 hrs to hydrolyze theprecursor. Then the solutions were refluxed at 92oC for 20 hrs to form a boehmite precipitate. The particle size of the boehmitesols was controlled according to various experimental parameters, such as acid types and acid concentrations. The topmost SiClayer was formed on top of the intermediate γ-Al2O3 by pyrolysis of a SiC precursor, polycarbosilane, in an Ar atmosphere. Theresulting amorphous SiC-on-Al2O3 composite membrane pyrolyzed at 900oC possessed a high H2 permeability of 3.61×10−7mol·m−2·s−1·Pa−1 and the H2/CO2 selectivity was much higher than the theoretical value of 4.69 in all permeation temperatureranges. Gas permeabilities through a SiC membrane are affected by Knudsen diffusion and a surface diffusion mechanism,which are based on the molecular weight of gas species and movement of adsorbed gas molecules on the surface of the pores.