This research scrutinized the effect of adding MIL-100 (Fe) metal-organic frameworks (MOFs) on the PEBAX membranes in two grades, 1657 and 2533. Initially, the intended membranes were synthesized by the solution-casting method. Then, XRD and SEM were applied to examine the influence of adding MIL-100 (Fe) to the structure of both membranes. Consequently, the separation function of the pair gases of CO2/CH4, CO2/N2, and CO2/O2 and their permeability were considered at the pressure of 3.5 bar and temperature of 25 ℃. Eventually, their function was compared by Robeson diagrams of 1991 and 2008. According to Robeson diagrams, the comparison outcomes indicated that the PEBAX1657/MIL-100 (Fe) and PEBAX2533/MIL-100 (Fe) membranes containing 5% of MOF represent better performance in separating CO2/CH4. However, their function for separating the considered gases requires more modifications.