Carbon dioxide and nitrogen transport properties of cardo polymers, i.e. polyamide, polycarbonate, polyimide, polysulfone and commercial polymers were investigated. These cardo polymers contain bis(phenyl)fluorene moiety as the cardo unit. Further, a variety of cardo polyimides were prepared from various dianhydrides to study the relationship between polymer rigidity and the gas transport properties. The cardo polymers showed larger permeabilities than those of commercial polymers because of a larger gas solubility. On the other hand, the gas diffusivity of the cardo polymers was nearly equal to that of the commercial polymers, in spite of the introduction of the bulky moiety. The most rigid polyimide showed the largest carbon dioxide permeability coefficient of 130 Barter (1 Barrer = 1 x 10(-10) cm(-3) (STP) cm (cm(2) s cmHg)(-1)), with large perm selectivity, P(CO2)/P(N-2), of 34. The bulky cardo moiety had the effect of increasing the glass transition temperature and d-spacing. Gas permeability, diffusivity and solubility of the cardo polyimides were well correlated to their fractional free volume (FFV). The rigid polyimide showed a large FFV, and consequently showed large gas permeability, diffusivity and solubility. On the other hand, polyamide, which has hydrogen bond, deviates from the diffusivity-FFV correlation of polyintides. The magnitude of gas permeability was mainly attributed to that of gas diffusivity, whereas the magnitude of permselectivity of carbon dioxide over nitrogen was attributed to that of solubility selectivity.