Abstract <p>In this study, the optimal degree of polymerization of polyvinyl alcohol (PVA) and appropriate carbonate content necessary to enhance the separation performance of a CO₂ separation membrane were determined. The membrane was composed of a composite polymer of PVA, which is known for its gas barrier properties, and sodium polyacrylate (PAANa), which acts as a water-absorbing agent. The PVA/PAANa membranes exhibited pressure resistance even without a cross-linking agent. To further improve the separation performance, membranes were prepared using PVA with four different degrees of polymerization (400–600, 1500–1800, 2000, and 3100–3900), and their separation capabilities were evaluated. Additionally, the optimal amount of caesium carbonate that enhances CO₂ permeance was determined. It was found that separation membranes made from PVA with a degree of polymerization of 1500-2000 exhibited higher separation performance. In particular, separation membranes fabricated with PVA with a degree of polymerization of 2000 showed the best separation performance. As a result, a high-performance CO₂ separation membrane was successfully developed, achieving a CO₂ separation performance of approximately 3.2E-10 (m³(STP)/(m² s Pa)) and a CO₂/He selectivity 700.</p>