Polymeric membranes containing sulfonated and fluorinated poly (ether ether ketone) were prepared by solution casting method. The monomers were pre-sulfonated before the polymerization to avoid the side effects of polymer post-sulfonation, like low degree of sulfonation and poor mechanical and thermal properties. The degree of sulfonation was varied from 20% to 40% to study its influence on the membrane performance. Pure and mixed gas permeation experiments were performed to evaluate the potential of this novel polymer in separation of CO2 from mixtures containing CH4 and N-2. Increasing degree of sulfonation improved the CO2 permeability and selectivity for both gas pairs. The incorporation of fluorinated groups further enhanced the performance of membranes by simultaneous increase in gas permeability and selectivity. Diffusion and solubility measurements were also performed in order to get further insight into the role of sulfonic and fluorinated groups in membrane performance. The comparison of results with literature revealed the promising characteristics of the polymer in industrially relevant gas separations. (C) 2016 Elsevier B.V. All rights reserved.