Among gas separation materials, carbon membrane exhibits the most interesting performance in terms of selectivity, stability, and gas permeance. By controlling and optimizing carbonization environment, excellent gas separation performances can be achieved. In this study, tubular supported carbon membrane was prepared using Matrimid as polymeric precursor. In order to produce high performance carbon membrane, the effect of carbonization conditions on the gas permeation properties was investigated. The polymer solution was coated on the surface of the tubular support by using dip-coating method. Carbon membranes were fabricated by heat treatment process under controlled carbonization environments; Ar or N2. Pure gas permeation tests were performed using CO2, CH4, and N2 at room temperature with pressure 8 bar. Based on the results, the highest CO2/CH4 and selectivity of 87.34 and CO2/N2 selectivity of 79.60 were obtained by carbon membrane carbonized under Ar gas. Despite the higher carbonization temperature, the carbonization under Ar created more permeable pores as compared to N2 environment.