Composite carbon membranes were prepared from poly (phthalazinone ether sulfone ketone) (PPESK) by incorporating with polyvinylpyrrolidone (PVP) or zeolite (ZSM-5) through stabilization and pyrolysis processes. The thermal stability of composite polymeric membranes was measured by thermal gravimetric analysis. The resultant composite carbon membranes were characterized by scanning electron microscopy, X-ray diffraction and gas permeation technique, respectively. The results illustrated that the thermal stability of composite polymeric membranes was enhanced by addition of ZSM-5 or reduced by PVP. For ZSM-5 or PVP composite carbon membranes prepared at 650 degrees C, the O-2 permeability is 199.70 Barrer or 124.89 Barrer, and the O-2/N-2 selectivity is 10.3 or 4.2, respectively. Compared with carbon membranes from pure PPESK, the O-2 permeability of ZSM-5 or PVP composite carbon membranes increases by 18.5 or 11.6 times, together with the O-2/N-2 selectivity decreasing by 35.2% or 73.6%, respectively. The gas separation mechanism of composite carbon membranes is molecular sieving. Adsorption effect also plays a significant role for CO2 permeating through ZSM-5 composite carbon membranes. (c) 2007 Elsevier B.V. All rights reserved.