Composite membranes were prepared by coating of perfluorinated copolymer Hyfon((R)) AD60x on a support of hollow fibre ultrafiltration membrane. Two types of polymer were used for the support: a glassy amorphous poly(ether ether ketone) and a crystalline partially oxidized acrylonitrile-vinylacetate copolymer. Hollow fibre membranes were prepared by the dry-wet spinning method. The pure gas transport properties of the uncoated and the coated membranes were studied for oxygen, nitrogen, methane, helium and carbon dioxide. A dense flat membrane was prepared by solvent evaporation for determination of the diffusion coefficient and solubility of various gases in Hyflon.