With the rapid growth of economics, carbon dioxide (CO2) gases are being emitted in bulk into the atmosphere contributing to the current global warming issues. Thus, membrane separation technology was implemented due to its notable benefits of simple operation, cost savings, and high efficiency in CO2 separation. In this study, the cellulose acetate butyrate (CAB) membrane was synthesized from CAB polymers of molecular weights (M-n) 12,000 and 65,000, while the effects of casting thickness and solvent evaporation time during membrane fabrication were studied. The optimal casting thickness and solvent evaporation time were obtained at 250 mu m and 5 min respectively, whereas the CO2 permeance and CO2/N-2 selectivity were obtained at 106.87 +/- 1.03 GPU and 6.948 +/- 0.081, respectively. Eventually, this newly developed CAB membrane is expected to benefit the industrial sectors by reducing the CO2 emissions with improved efficiencies in gas separation.