Abstract: Disclosed is an asymmetric gas separation membrane made of a soluble aromatic polyimide having a specific repeating unit, the soluble aromatic polyimide including: as a tetracarboxylic acid component, a biphenyl structure and a phenyl structure; as a diamine component, a 3,3?-diaminodiphenyl sulphone and a diaminodibenzothiophene, a diaminodibenzothiophene=5,5-dioxide, a diaminothioxanthene-10,10-dione, or a diaminothioxanthene-9,10,10-trione. Disclosed is a method for selectively separating and recovering a specific gas species from a mixed gas composed of a plurality of gas species using the asymmetric gas separation membrane, a method for selectively separating and recovering a nitrogen-rich gas from air using the asymmetric gas separation membrane, and a method for selectively separating carbon dioxide gas from a mixed gas containing carbon dioxide and methane and recovering methane-rich gas using the asymmetric gas separation membrane.