Highly selective separation of CO2 from its methane-containing binary gas mixture can be achieved by using Poly(ether-block-amide) (PEBAX) mixed matrix membranes (MMMs). According to FESEM and AFM analyses, silica-based nanoparticles were homogenously integrated within the polymer matrix, facilitating penetration of CO2 through the membrane while acting as barrier for methane gas. The membrane containing 4.6 wt% fumed silica (FS) (PEBAX/4.6 wt% FS) exhibits astonishing selectivity results where binary gas mixture of CO2/CH4 was used as feed gas. As detected by gas chromatography, in the permeate side, data showed a significant increase of CO2 permeance, while CH4 transport through the mixed matrix membrane was not detectable. Moreover, PEBAX/4.6 wt% FS greatly exceeds the Robeson limit. According to data reported on CO2/CH4 gas pair separation in the literature, the results achieved in this work are beyond those data reported in the literature, particularly when PEBAX/4.6 wt% FS membrane was utilized. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.