In recent years, carbon dioxide (CO2) emission has increased significantly. To overcome this issue, carbon capture and storage was implemented to remove CO2 due to its low energy consumption and economic advantages. As a result, membrane technology was introduced as one of the technologies for CO2 separation to capture CO2 from industrial processes. Cellulose acetate butyrate (CAB) was selected as the material for polymeric membrane due to its high CO2 solubility. The CAB membrane was fabricated by blending two CAB polymers at different molecular weights of 70000 and 65000 using the wet-phase inversion method. A study of the parameter was carried out as it affected the structure and separation performance of the membrane in particular, polymer concentration. The results showed the satisfactory performance of CAB membrane blended with molecular weights of 70000 and 65000 at a ratio of 40:60 (M3) where, the CO2 permeance, nitrogen (N2) permeance and CO2/N2 selectivity were 26.39 GPU, 7.73 GPU and 3.41 GPU, respectively. Hence, it is expected that this research may apply to membrane gas separation in industries such as power plants to separate CO2 from exhaust gas and reduce CO2 emissions.