Membrane-based CO2 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 CO2 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 (R) 1657 matrices to form mixed matrix membranes. The resulting membrane exhibits significantly improved CO2 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 CO2/N-2 and CO2/CH4 was also evaluated. The separation performance for CO2/CH4 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. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.