Among the carbon dioxide (CO2) separation methods, the membrane separation technology has been mostly applied to reduce the CO2 emission. Since most CO2 are emitted from power generation plants, the CO2/nitrogen (N2) separation was selected. In this project, the blend cellulose acetate (CA) membranes were prepared by mixing CA with 39 acetyl concentration (CA-39) and 56 acetyl content (CA-56) through the wet-phase inversion method. The CO2/N2 separation performance was determined by evaluating the permeation of gases and the CO2/N2 selectivity by modifying the polymer concentration. The characterisation of the membrane was carried out by using the scanning electron spectrometry (SEM) and attenuated total reflectance Fourier transform infrared spectrometry analysis (ATR-FTIR). The optimal membrane obtained was M3 with polymer concentration of 4:6 (CA-39:CA-56) that had defect-free membrane surface with smooth dense skin layer. The functional groups present enhanced the gas permeance rate. With regards to the gas permeation test, M3 presented the best CO2/N2 separation performance with CO2 permeance of 99.26 ± 3.08 GPU, N2 permeance of 87.12 ± 0.81 GPU and CO2/N2 selectivity of 1.139 ± 0.037. It is expected that the results obtained from this work can be applied to industries, such as the gas separation field or power generation plant, in order to reduce CO2 emission. © Penerbit Universiti Sains Malaysia, 2020.