In this study Pebax copolymer, 1-Butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) ionic liquid and Ag nanoparticles were used to fabricate composite and mixed matrix membranes. Permeability and selectivity of the prepared membranes were measured at temperature of 35°C and pressure of 6bar to investigate optimum compositions of the nanoparticles and the IL. The results revealed that the best performance of the composite and mixed matrix membranes for CO2 separation were at 1wt% Ag loading and 50wt% IL content, respectively.