Here, we report for the first time the fabrication of a glassy polymer/nickel oxide hybrid membrane as a gas separation membrane. A PI (Matrimid) is used as a continuous phase, and nickel oxide nanoparticles (NiO) were utilized as a dispersed phase. The structure of mixed matrix (MMMs) and pure Matrimid membranes are investigated by employing various characterization techniques including scanning electron microscopy (SEM), Fourier transforms infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and tensile stress-strain to characterize the NiO nanoparticles. The effect of NiO nanoparticles content (0-5 wt%) on gas permeability of pure CO2, CH4, O-2, and N-2 gases at different operating temperatures (24-40 degrees C) and feed pressures (1-5 bar) were surveyed. The results revealed that the CO2 permeability almost did not change and CO2/CH4 selectivity of PI was enhanced with low-level loadings of NiO while the gas permeability of N-2, CH4, and O-2 was reduced. Our results indicated that since NiO nanoparticles have high interaction with CO2 as Lewis pairs, they have high potential to improve the gas permeability properties of polymer-based membranes. This approach allows predicting the gas transport properties, structure/solubility quantitative relationships of different gases, especially CO2 through the MMMs system. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.