A three-dimensional NiDOBDC/GO composite with an optimized accessible surface area was successfully synthesized and incorporated into a polyimide membrane to improve CO2/CH4 separation performance while keeping good mechanical strength. A significant increase in CO2/CH4 selectivity (59%) was observed for the case of 20% NiDOBDC/GO composite in Matrimid (R) membrane, without sacrificing CO2 permeability. Furthermore, the incorporation of the NiDOBDC/GO composite in a polymeric membrane was found to improve the overall mechanical strength of resulting mixed-matrix membranes. Therefore, the addition of the nanocomposites as fillers in polymeric membranes is proposed as a promising strategy to realize major improvements in CO2/CH4 separation. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.