Membranes have been developed for separation of specific gas from other gas molecules. Tube type ceramic was used for substrate. Silica membranes derived from tetramethoxysilane (TMOS), phenyltrimethoxysilane (PhTMS) and 3-aminopropylmethyldiethoxysilane (APMDES) were synthesized by chemical vapor deposition (CVD) method at 650 degrees C. Permeation experiments with H-2, CO2 and N-2 with ceramic membranes were performed to determine the gas transport characteristics. H-2/N-2 selectivities of TMOS, PhTMS and APMDES derived membranes were decreased by 1265, 633 and 100. And CO2/N-2 selectivities of TMOS, PhTMS and APMDES derived membrane were increased by 3, 5 and 20. It is suggested that whether the intermediate contained living groups has a large effect on the enlargement of the pore size of amorphous silica membranes.