Carbon membrane has attracted researchers’ attention as it is superior in terms of its gas separation performance. In this study, the composition of polymer precursor in the dope solution was investigated based on carbon membrane performance. P84 polyimide was chosen as the polymer precursor as it fulfils the requirement for carbon membrane properties. By varying the polymer precursor composition (6, 9, 12, and 15 wt.%), P84 was stirred in NMP solvent until homogenous solution was formed. Commercialised alumina disc was coated via spray coating method at 1 bar at room temperature. The disc supported polymeric membrane was carbonised at 700 °C under nitrogen (200 ml/min) with heating rate of 3 °C/min. The carbon membrane was analysed via SEM. Gas permeation tests were performed using pure O2 and N2 at 4 bar at room temperature. The selectivity of 3.7 was obtained using the disc supported carbon membrane for O2/N2. The optimum polymer composition in this study was obtained by 12 wt.% of P84.