The sorption and permeation properties of CO₂ and CH₄ for synthesized brominated polysulfone, BPSf(bromobisphenol A polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone), MPSf (bisphenol A methylated polysulfone) and TMSPSf (bisphenol A trimethylsilylated polysulfone) to investigate the structure-property relationships. Especially, the effect of polarity of substituents on the transport properties was studied. The effect of operating pressure on the permeation properties of polysulfones was examined. The permeation properties far a mixture of CO₂ and CH₄ were also measured, and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to the dual mode model. The permeability coefficients of each gas of a binary mixture are less than those of pure gases, and the extent of reduction in permeability coefficient is larger far less permeable polymer. The ideal separation factor for four polysulfones increases in the following order : TMSPSf< PSf< BPSf< MPSf. The ideal separation factor for BPSf is higher than other polysulfones having similar permeability coefficients of CO₂ with BPSf. It can be explained that the strong polarity of bromine in BPSf increases cohesive energy density of polymer, and reduces the chain packing-inhibiting ability. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is not consistent with the permeability coefficient.