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Using hydrothermal synthesis, a highly hydrophobic DDR-type zeolite membrane was prepared on the outer surface of a porous -alumina tube. The results of this study show that it is useful for CO2/CH4separation. Single-gas permeation for CO2, CH4, H2, He, N2, and O2, and CO2/CH4binary gas permeation, were measured, respectively, at pressures up to 5 and 2 MPa. The respective single-gas permeances of CO2and CH4at 298 K at a feed pressure of 0.2 MPa and a permeate pressure of 0.1 MPa were 4.2 × 10-7and 1.2 × 10-9mol m-2s-1Pa-1; the ideal selectivity for CO2/CH4was 340. The permeances were in the following order:  CO2> H2> He > O2> N2> CH4. Single-gas permeance was dependent on the relative molecular size of the DDR pore diameter. However, CO2permeance dominated the adsorption affinity to the pore wall of DDR zeolite. In mixed-gas permeation experiments using the sweep method, the DDR-type zeolite membrane showed high selectivity for CO2/CH4mixtures of 200 and high CO2permeance of 3.0 × 10-7mol m-2s-1Pa-1at 298 K with a feed pressure of 0.2 MPa. Furthermore, the DDR zeolite membranes were compared to other zeolite membranes for evaluation of their CO2/CH4selectivity and CO2permeance; the DDR-type zeolite membranes show better CO2/CH4separation and CO2permeance. [ABSTRACT FROM AUTHOR]