Graphene oxide (GO) nanosheets and zeolitic imidazole frameworks (ZIF-301) were synergistically integrated to glassy polysulfone (PSF) to prepare mixed-matrix membranes (MMMs) for CO2 separation from post combustion flue gas. Both nanofillers were incorporated in PSF in varying compositions using solution-casting technique to optimize CO2 separation performance of composite membranes form dry and wet gases. The flexible MMMs rendered homogeneous dispersion of nanofillers, improved polymer filler adhesion, and thermally stable structure. Gas sorption analyses along with dry and wet gas permeation experiments showed improved CO2 permeability and CO2/N-2 selectivity of MMMs due to synergistic effect of nanofillers. The prepared MMMs demonstrated about four- and three-folds increment in CO2 permeability CO2/N-2 selectivity respectively as compared to that of bare PSF membrane. Separation performance of composite membranes was found to better than already existing membranes; they were stable in presence of water and performance was not affected by humid conditions. (C) 2016 Elsevier B.V. All rights reserved.