Sorption of single-component vapors of benzene (Bz), n-hexane (Hx), and cyclohexane (Cx), and of binary liquid mixtures of Bz/Hx and Bz/Cx in a polyimide from 3,3',4,4'-diphenylsulfone-tetracarboxylic dianhydride (DSDA) and 2,8(6)-dimethyl-3,7-diaminobenzothiophene-5,5-dioxide (DDBT) were investigated in detail at 333 K. Sorption and desorption of vapors followed the non-Fickian kinetics and the sorption isotherms were concave to the vapor activity. For the binary liquids, the sorption isotherms of the Bz component were concave to the Bz composition in feed, whereas those of Hx and Cx were convex because of competitive sorption. As a result, the solubility selectivity was much larger than the sorption ratio of pure liquids. The concentration-averaged diffusion coefficients of Bz ((D) over bar (Bz)) and Hx ((D) over bar (Hz)) were evaluated using the sorption and pervaporation data of the polyimide membrane toward the binary mixtures. A kind of coupling effect of the coexisting component on D was observed. That is, (D) over bar of penetrant with smaller molecular size (Hx and Bz for Bz/Hx and Bz/Cx systems, respectively) was reduced by the presence of penetrant with larger molecular size (Bz and Cx, respectively) and vice versa. (D) over bar (Bz) was similar to (D) over bar (Hx), but much larger than (D) over bar (Cx). The difference in PV behavior between Bz/Hx and Bz/Cx systems for glassy polymer membranes was understood based on the aforementioned features of sorption and diffusion.