Carbon molecular sieve membrane (CMSM) was prepared by pyrolysis of phenol formaldehyde novolac resin (PFNR) blended with poly(ethylene glycol) (PEG). The carbon structures and the gas permeation properties of the CMSM pyrolyzed at 800 degrees C were characterized in terms of the different weight ratio of PEG to PFNR and different molecular weight of PEG. The thermogravimetric analysis indicated that the copyrolysis in the PEG/PFNR appears at temperature of 400 degrees C. The nitrogen adsorption isotherm of the CMSM showed that the weight ratio of PEG/PFNR and molecular weight of PEG significantly affect the average pore volume of the CMSM. These results confirmed that PEG is a significant pore-forming agent in the CMSM for the micropores forming during pyrolysis, which will increase the pathways of diffusion for the transport of gas molecules through the CMSM. The CMSM prepared exhibits an enhanced H-2 and O-2 as permeability from 2.4 x 10(-9) and 6.4 x 10(-11) to 8.0 x 10(-9) and 1.8 x 10(-11) mol m(-2) s(-1) Pa-1, and the H-2/N-2 and O-2/N-2 selectivity of the CMSM derived from PEG/PFNR blends decreases from 471.3 and 12.8 to a minimum of 284.6 and 6.2, respectively, with addition of PEG with molecular weight of 10,000 to PFNR in weight ratio of 0.05. (c) 2006 Elsevier B.V. All rights reserved.