Mixed matrix membranes (MMMs) were fabricated by incorporating carbon nanotubes (CNTs) and graphene oxide (GO) into a Matrimid^® matrix to improve CO₂ separation performance. The combination of CNTs and GO exerted a favorable synergistic effect on the permselectivity of membranes. The extraordinary smooth walls of CNTs acted as a highway to render high permeability, whereas the graphene oxide nanosheets acted as a selective barrier to render high selectivity through the hydroxyl and carboxyl groups on GO surface in MMMs. The MMMs doped with both CNTs and GO had better gas separation performance than those doped with only CNTs or GO. Efficient CO₂ transport pathways were constructed by homogeneous dispersion of CNTs and GO within MMMs, leading to both enhanced permeability and selectivity. The membrane combining 5 wt% of CNTs and 5 wt% of GO (Matrimid^®-CNTs/GO-5/5) displayed the optimum performance with a CO₂ permeability of 38.07 Barrer, a CO₂/CH₄ selectivity of 84.60 and a CO₂/N₂ selectivity of 81.00. Compared to pure Matrimid^® membrane, the CO₂ permeability, CO₂/CH₄ selectivity and CO₂/N₂ selectivity of the Matrimid^®-CNTs/GO-5/5 membrane were increased by 331%, 149%, 147%, respectively.