Metal-organic frameworks are appealing candidates for molecular separation particularly for CO2 and other molecular mixture separation because of the high porosity, structural flexibility, pore size and chemical tailorability as highlighted in several reviews.1-5 In the form of powders, MOFs have exhibited an unprecedented CO2 adsorption capacity/selectivity and high CO2 adsorptive separation efficiency from N2 and CH4. The excellent preferential CO2 adsorption ability are expected to lead to high CO2 permselectivity over other gases for MOFs membranes. However, so far only the MOF-5 membrane reported by Zhao et al. showed efficient separation for CO2/N2 mixtures under high pressure and CO2 content conditions.6-7 Instead, other reported MOFs membranes including small and large pore size MOFs membranes have so far shown a poor CO2/N2 separation selectivity around 1 for either single gas or mixture system despite of their high adsorption selectivity.8-11 There is a long way to explore MOF membranes with high performance for CO2 capture. In the present work, a continuous and thin amine-decorated microporous metal-organic framework CAU-1 membrane on asymmetric a-Al2O3 support was synthesized and explored for CO2 separation. The obtained CAU-1 membrane was of 2C3μm thin and exhibited a high CO2 permeance of up to 1.34 °Á 10-6 mol m-2 s-1 Pa-1 and a CO2-N2 selectivity of 17.4-22.8 for CO2-N2 mixtures, demonstrating for the first time that aminofunctionalized MOF membranes can provide high CO2CN2 selectivity and possess the potential for CO2 capture from flue gas12. Separation of other molecular mixture will be studied as well.