Mixed-matrix membranes (MMMs) composed of suitable CO2-philic polymers and fillers can be attractive candidates for CO2/CH4 and CO2/N2 separation due to their high CO2 permeability, good thermochemical stability, low fabrication cost, and fast production process. In this research, a novel ternary MMM was fabricated via the blending of poly (amide 12-b-ethylene oxide) (PEBAX-1074) with polyethylene glycol (PEG-200) and magnesium oxide (MgO) nanoparticles mixture. The effects of various loadings of the fillers on CO2, N2, and CH4 permeability values through the membranes were studied. Permeation of CO2, N2, and CH4 gases through the resultant membranes at pressures of 2, 4, 6, 8, and 10 bar and temperatures of 25, 35, 45, and 55 oC revealed the superiority of the MMMs for CO2/CH4 and CO2/N2 separation in comparison with the pristine membranes. Particularly, at 25 oC and 2 bar, the CO2 permeability, as well as ideal CO2/CH4 and CO2/N2 selectivity of the optimized MMM containing 40 wt% of PEG-200 and 8 wt% of MgO nanoparticles, rose to 210.1 Barrer, 24.9 and 60.9, corresponding to enhancement of around 225%, 23% and 24% of the CO2 permeability and selectivity compared to the neat membrane, respectively. Thus, the fabricated MMM has a satisfying potential to separate CO2 from N2.