Segmented polyurethane and polyurethane urea, containing soft segments such as polydimethylsiloxane (PDMS), polytetramethylene oxide (PTMO), and polyethylene oxide-polypropylene oxide triblock copolymer (PEO-PPO-PEO), were synthesized with a wide range of monomer concentrations. Dense membranes with 30-40 mum in thickness prepared by casting 20 wt.% N,N-dimethylformamide (DMF) solutions onto glass plate were examined for the separation of toluene vapor from nitrogen stream. Equilibrium liquid sorption behaviors of synthetic membranes were carried out by determining the amount of liquid toluene absorbed in the films at 25 degreesC. The vapor permeability of toluene through the PTMO/PDMS based polyurethane urea membranes were higher than those measured in PEO-PPO-PEO based polyurethane membranes due to plasticization by toluene vapor. In the case of the PTMO/PDMS based polyurethane urea membranes. the permeability of nitrogen increased and then the toluene/N-2 selectivity was lowered relative to those for PEO-PPO-PEO based polyurethane membranes due to plasticization of polymer. Up to the feed-flow rate of 250 ml min(-1), the toluene fluxes obtained in all the membranes showed a linear dependence on the saturated feed concentration, The polyurethane urea membranes containing PTMO/PDMS mixed soft segment performed best with toluene separation, with toluene/N-2 selectivity ranging from 70 to 140 and the pressure-normalized permeability as high as 17,500 Barrer when the saturated toluene feeds were operated at 25 degreesC and a downstream pressure of 0.5 cmHg.