3-Di-n-butyl-2-mthylimidazolium chloride (DnBMCl) ionic liquid (IL) was synthesized and used for modification of Pebax 1657 surface. ZIF-8 particles synthesized by different molar ratios of precursors, were introduced into the matrix of IL-Pebax 1657 for fabrication of mixed matrix membranes (MMMs) by coating method. Synthesized ZIF-8 particles were characterized using laser particle size analyzer, SEM, XRD and N-2 adsorption. SEM, DSC, FTIR, C-13 NMR, TGA and gas permeation tests were applied for characterization and performance evaluation of MMMs. The modification of Pebax 1657 with DnBMCl lead to formation of possible Carbon Carbon bonds between Pebax 1657 and DnBMCl and also between ZIF-8 and DnBMCl. Pure gas permeation tests showed that the higher ideal selectivities of CO2/CH4, CO2/N-2 and CO2/H-2 were observed for DnBMCl-modified MMMs compared to unmodified MMMs and neat Pebax 1657 membrane. Plasticization lead to inferior CO2 separation ability of MMMs in mixed gas condition compared to pure gas test. The DnBMCl-modified Pebax 1657/ZIF-8 MMMs showed superior CO2/CH4, CO2/N-2 selectivities at feed pressures of 2 and 4 bar.