Zeolite crystals as inorganic fillers were widely applied in fabricating mixed matrix membranes (MMMs) for CO₂ separation. The poor filler-matrix interaction and the aggregation of high-loaded fillers in MMMs restrict their advantage of overcoming the trade-off limitation between permeability and selectivity. The novel MMMs with two-dimensional (2D) MFI nanosheets as inorganic fillers and Pebax MH 1657 as the matrix were synthesized and applied to achieve an efficient separation of CO₂/CH₄ gas mixture for the first time. The large interfacial contact areas between MFI nanosheets and Pebax matrix improve their compatibility to form defect-free MMMs with better mechanical properties. The high-aspect-ratio MFI nanosheets function as solid and selective barriers to make MMMs possess a significant promotion in both CO₂ permeability and CO₂/CH₄ selectivity without the trade-off limitation. The MMM containing 5 wt% of MFI nanosheets exhibited the optimum performance with CO₂ permeability of 159.1 Barrer and CO₂/CH₄ selectivity of 27.4. The as-prepared MMMs showed an improvement of 63.5% in CO₂ permeability and 76.4% in CO₂/CH₄ selectivity, compared to pristine Pebax membranes.