Effects of pyrolysis and preparation conditions on the gas permeation properties of pyrolytic membranes derived from sulfortated phenolic resin were investigated. Pyrolysis temperature, dip-coating conditions and coating/pyrolysis (C/P) cycle had significant influence on the gas permeation properties of pyrolytic membranes. Membrane obtained under optimum preparation conditions exhibited O-2 pertneance of 30GPU and ideal O2N2 separation factor of 12 at 35degreesC, which are comparable to the O-2/N-2 separation performances of carbon molecular sieve (CMS) membranes on the upper-bound line in the plots of permeance versus selectivity. N-2 adsorption and desorption at 77 K suggested that the pore structures of CMS membranes pyrolyzed around 500degreesC seemed to be made up of interconnected pores with different size and shape. (C) 2003 Elsevier Science B.V. All rights reserved.