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The gas separation membrane is operated in condition of high temperature and corrosiveness.So thermostable polymers were needed.One of the most thermostable polymers,the polyimide based on aromatic structures has been especially studied because of a good thermal stability,chemical resistance,excellent mechanical strength,and gas properties [1].But the polyimide shows low permeability,a lot of study on some changes in the chemical structure of aromatic polyimide was performed to improve gas permeability and selectivity [2].In this study,the copolyimides were studied because copolymer having various functional groups strengthens the strength of homopolyimide and make up for its weakness [3].Copolyimides were synthesized using various monomers with both bulky cardo group and rigid group via chemical imidization.Chemical cyclodehydration was conducted by adding a mixture of acetic anhydride and triethylamine.Polyimide is possible to make by imidization at low temperature and polyimide obtained via chemical imidization has a good solubility.So it is expected to be a higher processibility compared with polyimide obtained via thermal imidization.The chemical structures of prepared copolyimides were confirmed by FT-IR and NMR.The various characteristics of copolyimides prepared with different mole ratio were evaluated by TGA,DSC,XRD.The copolyimide membranes were prepared by solvent evaporation method and the gas transport properties of membranes were determined by time-lag method at 30 °C.Also,the chemicophysical and gas properties of copolyimide membranes were measured and compared with homopolyimides.