Gas sorption and transport properties of ozone-treated polysulfone (PSF) were investigated. Ozone treatment of PSF was made by the exposure of PSF to ozone-containing oxygen for certain hours. Gas sorption isotherms for PSF were made for N-2, O-2, CH4 and CO2, and sorption data were analyzed by the dual-mode sorption model. Overall sorption for each gas except CO2 decreased after ozone treatment of PSF. Dual sorption parameters k(D) and b decreased and C-H(1) increased for all the H gases after ozone treatment. Diffusion coefficients were calculated by the equation P = DS. The diffusion coefficient of each gas decreased after ozone treatment. The increase in the ideal selectivity of ozone-treated PSF, alpha(O-2/N-2) was more affected by the difference in diffusion coefficients between ozone-treated PSF and untreated PSF than by the difference in solubility coefficients. However, alpha(CO2/CH4) was affected by differences in solubility coefficients as well as diffusion coefficients. (C) 2003 Published by Elsevier Science B.V.