Thianthrene-2,3,7,8-tetracarboxylic dianhydride-5,5,10,10-tetraoxide (TADATO), a dianhydride having two sulfonyls between two phenyl rings, was synthesized and polymerized with several diamines by a two-step method. Tough polyimide membranes were obtained with flexible diamines but not with rigid diamines. Most of TADATO-based polyimides are soluble in polar solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone. IR study confirmed that almost complete imidization of TADATO-based poly( amic acid) membranes could be achieved by thermal treatment at 100, 200, and 300 degrees C for each 1 h. In a series of polyimides based on 4,4＇-oxydianiline, the polyimide from TADATO showed higher gas permeability coefficient of CO2 and higher selectivities of CO2/N-2 and CO2/CH4 than those of polyimides from pyromellitic dianhydride and 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride, and was comparable to that from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride.