In this work, polyethersulfone (PES) based gas separation ionic liquid polymeric membranes (ILPMs) were synthesized. Ionic liquids 1-Ethyl-3-methylimidazolium dicyanamide EMIMDCA and 1-Ethyl-3-methylimidazolium tetrafluoroborate EMIMBF4 were incorporated in the dope solution at 10 weight % and flat sheet dense membranes were casted by dry phase inversion method. Morphology of the developed membranes was evaluated using field emission scanning electron microscope (FESEM) and thermal stability was evaluated using thermogravimetric analysis (TGA). The gas permeation experiments were performed at ambient room temperature and 2 bar pressure. FESEM images showed a dense structure which indicates the compatibility of polymer and ionic liquids. The CO2 gas permeability of the synthesized ILPMs were increased by blending ionic liquids in polymer matrix due to high solubility and affinity of CO2 in EMIMDCA and EMIM BF4 ionic liquids. Membrane PES+IL1 (10%) showed nearly 23.5 folds increase in CO2 gas permeability compared to pure polyethersulfone membrane. These ILPMs have immense potential for CO2 separation from natural gas. © 2019 Elsevier Ltd. All rights reserved.