A new class of multi-wall carbon nanotubes (MWCNTs)/carbon nanocomposite thin films Was Successfully prepared by incorporating (MWCNTs) into polyimide (PI) precursor solution. The carbon films were obtained in only one coating step by spin-coating technique on a macroporous alumina substrate and were pyrolyzed at 773 K. The structure and single gas permeation properties of PI-based carbon membranes incorporated with or without MWCNTs were investigated. From the FE-SEM images, the pure carbon membranes have a thin dense permselective layer with few closed pores while the permselective layer of the MWCNTs/carbon nanocomposite thin films are porous due to the structure of nanotubes. The MWCNTs/carbon nanocomposite thin films exhibited that the ideal carbon dioxide flux Was 866.6 Barrer (1 Barter = 1 x 10(-10) cm(3) (STP) cm cm(-1) s(-1) cm Hg-1) and the separation factor of CO2/N-2 was 4.1 at room temperature and 1 atm, which was 2-4 times of magnitude higher than that of pure carbon membrane prepared by the same procedures and conditions.