The degradation of Kapton polyimide leads to a carbon membrane with a dense surface layer suitable for gas permeations. An integral asymmetric capillary carbon membrane was prepared by coagulation of a polyamic acid solution which was imidized to a Kapton capillary and finally pyrolized to a capillary carbon membrane. Various preparation conditions have been studied. Single and mixed gas permeation experiments had been performed. The carbon membrane showed high permselectivities of 2000 for He/N-2 and about 1000 for H-2/N-2 at O degrees C, respectively. Even for a high temperature of about 250 degrees C the He/N-2 selectivity reached 170.