PURPOSE: To provide a permselective gas permeable membrane having excellent permselectivity and high membrane strength and available for obtaining oxygen rich air, by forming a membrane from a polymer having a perfluoroalkyl group- containing surfactant compound therein.

CONSTITUTION: For example, phenylchlorophenyl ladder type polysiloxane is dissolved in a solvent mixture consisting of tetrahydrofran and toluene, and, for example, a perfluoroalkyl group-containing surfactant represented by formula is added to the resulting solution to prepare a uniform solution which is, in turn, formed into a membrane by a casting method. In this case, if a plasticizer such as an epoxy, polyester, phthalic acid, trimellitic acid or phosphate type one is used together, the compatibility of the perfluoroalkyl group-containing surfactant to the polymer is enhanced.