A membrane with an oxygen-binding capability and nanometer thickness was prepared by complexing cobalt-phthalocyanine as an oxygen carrier with the copolymer of vinylimidazole and octyl methacrylate. The complex showed reversible oxygen-binding in the solution state at low temperature. The permeability coefficient of oxygen (P-O2) through this membrane was much higher than that of nitrogen (P-N2) (P-O2/P-N2 > 20) and increased at lower upstream oxygen pressure. The facilitation of oxygen transport was augmented by increasing the concentration of the oxygen carrier, cobalt-phthalocyanine fixed in the membrane. (C) 2005 Elsevier B.V. All rights reserved.