An asymmetric carbon membrane was prepared by coating alcohol solution of novolac phenol-formaldehyde resin containing a little hexamine on a porous resin support from the same material. After drying in air for two days at room temperature, the coated support was heated at 150 degrees C for I h in air (heating rate: 0.5 degrees C/min) and then carbonized at 800 degrees C (heating rate: 0.5 degrees C/min) in Ar atmosphere. The support and the membrane layer were carbonized simultaneously. The coating-pyrolysis cycle only needed one time. SEM photographs showed the carbon membrane had an asymmetric structure formed by a dense skin layer with a thickness of around 35 mu m and a porous substrate. Pure gases of different molecular size (H-2, CO2, O-2, N-2 and CH4) were used to test the carbon membrane permeance property. The membrane has a good selectivity for H-2/N-2 and H-2/CH4 with H-2 permeance of 4.05 x 10(-6) cm(3) cm(-2) s(-1) cmHg(-1). The permeance is independent of pressure. The results indicate that the gases transport through the membrane according to molecular sieve mechanism. (c) 2007 Elsevier B.V. All rights reserved.