A hydrophobic metal organic framework (MOF) UiO-66-CH3 is prepared and its solvothermal stability is investigated in comparison to UiO-66. It is confirmed that the MOF stability is enhanced by introduction of the two methyl groups, while the water adsorption is reduced. Given its hydrophobicity and stability, UiO-66-CH3 is proposed as an attractive membrane material for gas separation under moisture conditions. The UiO-66-CH3 membrane is prepared on a 50 pm thin porous Ni support sheet for the first time by use of a secondary growth method. It is found that uniform seed coating on the support is necessary to form a continuous membrane. In addition to growth time and temperature, the presence of a modulator in the growth solution is found to be useful for controlling hydrothermal membrane growth on the seeded support. A dense, intergrown membrane layer is, formed by 24 h growth over a temperature range from 120 to 160 degrees C. The membrane surface comprises 500 nm octahedral crystals, which are supposed to grow out of the original 100 nm spherical seeding crystals. The separation characteristics of resulting membranes are tested with pure CO2, air, CO2/air mixture, and humid CO2/air mixture. CO2 permeance as high as 1.9 x 10(-6) mol/(m(2) s Pa) at 31 degrees C is obtained. Unlike the hydrophilic zeolite membranes, CO2 permeation through this membrane is not blocked by the presence of water vapor in the feed gas. The results suggest that this MOF is a promising membrane material worth further investigation for separation of CO2 and other small molecules from humid gas mixtures.