A porous alpha-alumina support tube, polished with a finely powdered X-type zeolite for use as seeds, was placed vertically in an autoclave containing an aqueous mixture of water glass and sodium aluminate. Hydrothermal synthesis was carried out at 90 degrees C for 24 h. A polycrystalline layer of Y-type zeolite was thus formed on the outer surface of the support tube. After washing and drying in air, permeances of single components and mixtures of CO2 and N-2, as well as CH4, C2H6, and SF6, were determined. The CO2 permeance was higher than that of N-2 at temperatures of 30-130 degrees C. When an equimolar mixture of CO2 and N-2 was fed into the feed side, the CO2 permeance was nearly equal to that for the single-component system and the N-2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. This was due to selective adsorption of CO2 in subnanometer micropores of the membrane. At 30 degrees C, the permeance of CO2 was higher than 10(-7) mol . m(-2). s(-1). Pa-1, and the permselectivity of CO2 to N-2 was 20-100.