NaY-type zeolite membranes were synthesized on a porous support tube by a hydrothermal process. The membranes were ion-exchanged with Li+ and K+ ions, and permeances through the membranes were determined for an equimolar mixture of CO2 and N-2, as well as for single-components thereof, at a temperature range of 0 - 400 degrees C. The permeance to CO2 showed a maximum at 100 degrees C, but CO2/N-2 selectivity decreased with increasing temperature. The zeolite membranes that were exchanged with K+ and Li+ ions gave higher and lower CO2/N-2 selectivities, respectively, than there found for the NaY-type membrane. The permeation properties of the ion-exchanged zeolite membranes were analyzed using a sorption - diffusion model. The high CO2/N-2 selectivity of the K-exchanged membranes can be explained by the decrease in N-2 sorptivity for the mixed feed.