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The in-depth investigation of the structure–property relationship in porous organic cages (POCs) for real gas mixture separation is both significant and challenging. In this work, we employed microenvironment modulation strategy to systematically regulate the gas adsorption and separation performance of POCs. The introduction of amino groups into the cavity of [2 + 4] lantern-shaped POC (CPOC-108) can effectively facilitate multiple host–guest interactions in confined cavities via forming hydrogen bond interactions. The as-prepared amino-functionalized POC (CPOC-108-NH₂) thus exhibits remarkably enhanced C₂H₂ and CO₂ adsorption capacities, especially for the more polarizable C₂H₂ gas, as well as higher C₂H₂/CO₂ selectivity in comparison to CPOC-108. More importantly, CPOC-108-NH₂ displays significantly improved separation performance for C₂H₂/CO₂ mixture, as evidenced by dynamic breakthrough experiments. This work provides an elegant example for a comparative study on C₂H₂/CO₂ separation properties between amino-functionalized and unsubstituted POCs, and may shed light on fine-tuning the cavity surfaces of POCs to rationally regulate their properties.