Membrane-based CO_2 separation is a promising alternative in terms of energy and environmental issues to other conventional techniques. Polyether-polyamide block copolymer(Pebax) membranes are promising for CO_2 separation because of their excellent selectivity, but limited by their moderate gas permeability. In this study,fresh-prepared zeolitic imidazolate framework-8(ZIF-8) nanocrystals were integrated into the Pebax?1657matrices to form mixed matrix membranes. The resulting membrane exhibits significantly improved CO_2permeability(as high as 300% increase), without the sacrifice of the selectivity, to the pristine polymer membrane. Several physical characterization techniques were employed to confirm the good interfacial interaction between ZIF-8 fillers and Pebax matrices. The effect of added ZIF-8 fillers on the transport mechanism through MMMs is also explored. Mixed-gas permeation for both CO_2/N_2 and CO_2/CH_4 was also evaluated. The separation performance for CO_2/CH_4 mixtures on the ZIF-8/Pebax MMMs is very close to the Roberson upper bound, and thus is technologically attractive for purification of natural gas. Membrane-based CO 2 separation is a promising alternative in terms of energy and environmental issues to other conventional techniques. Polyether-polyamide block copolymer (Pebax) membranes are promising for CO 2 separation because of their excellent selectivity, but limited by their moderate gas permeability. In This study, fresh-prepared zeolitic imidazolate framework-8 (ZIF-8) nanocrystals were integrated into the Pebax® 1657 matrices to form mixed matrix membranes. The resulting membrane exhibits significantly improved CO 2 permeability (as high as 300% increase), without the sacrifice of The selectivity to the pristine polymer membrane. Several physical characterization techniques were employed to confirm the good interfacial interaction between ZIF-8 fillers and Pebax matrices. The effect of added ZIF-8 fillers on the transport mechanism through MMMs is also explored. Mixed- gas permeation for both CO 2 / N_2 and CO_2 / CH_4 was also evaluated. The separation performance for CO_2 / CH_4 mixtu res on the ZIF-8 / Pebax MMMs is very close to the Roberson upper bound, and thus is technologically attractive for purification of natural gas.