A zeolite membrane was formed on a porous α-alumina support tube by hydrothermal reaction using a solution which was appropriate for the synthesis of ETS-4 zeolite. The morphology and x-ray diffraction pattern of the top surface of the support tube were consistent with those of the ETS-4 zeolite. The permeances to single-component H2, CO2, O2, N2, and CH4 were in the range (0.8–2.5)×10− 8 mol m− 2 sec− 1 Pa− 1, while those to n-C4H10 and iso-C4H10 were less than 10− 11 mol m− 2 sec− 1 Pa− 1. This suggests that the membrane functioned as a molecular sieve with pores smaller than 0.4 nm. At a permeation temperature of 310K, the ideal N2/O2 separation factor was 2.8, and the N2/O2 separation factor was 2.3 and 3.2 for a mixture of and 4, respectively. Thus, the membrane is nitrogen-selective and can be used to enrich the oxygen level in air, which is fed on the pressurized side, without much loss of compression energy.