In the separation of toluene-n-heptane mixture by liquid membrane, extractive solvents such as sulfolane, methyl sulfone and triethylene glycol were intermixed with membrane to improve the separability. Detailed analysis was carried out concerning the effects of such factors as the type and the concentration of extraction solvents and the contact time on the permeability and separation factor. As the extractive solvent concentration increased, the permeation of toluene and n-heptane increased. With 10 vol% of sulfolane a higher separation factor than with no sulfolane was achicved at the contact time of 10 minutes. The percentage of membrane breakup was smallest when the concentration of sodium lauryl sulfate was 0.5 wt% where the separation factor reached its highest value.