Interfacial void-free mixed-matrix membranes (MMMs) of polyimide (PI)/zeolite were developed using 13X and Linde type?A nano-zeolites and tested for gas separation purposes. Fabrication of a void-free polymer-zeolite interface was verified by the decreasing permeability developed by the MMMs for the examined gases, in comparison to the pure PI membrane. The molecular sieving effect introduced by zeolite?13X improved the CO2/N2 and CO2/CH4 selectivity of the MMMs. Separation tests indicated that the manufactured nanocomposite membrane with 30?% loading of 13X had the highest permselectivity for the gas pairs CO2/CH4 and CO2/N2 at the three examined feed pressures of 4, 8 and 12?atm.