Vapor permeation of a benzene and cyclohexane mixture was studied using a liquid membrane of triethylene glycol (TEG), which is supported on the surface of a microporous hydrophobic membrane. Permeation experiments were conducted using a flat-type membrane cell under the conditions of atmospheric pressure on the feed side and a vacuum on the permeate side. Mixed vapors of benzene/cyclobexane and water were fed into the membrane cell by a carrier gas. The benzene vapor preferentially permeated through the TEG liquid membrane, that is, the TEG liquid membrane had a selectivity for the aromatic hydrocarbon. The separation factor for benzene over cyclohexane was around 8. This selectivity corresponded to the vapor-liquid equilibrium of hydrocarbons dissolved in TEG. Adding a salt to the TEG liquid membrane caused an increasing aromatic selectivity as well as a decreasing vapor permeation rate. This effect was examined using various salts, which were formulated using alkali metal and halogen ions. A liquid membrane of a TEG and KCl mixture showed a separation factor of over 400. KCl was the most effective agent to enhance the benzene selectivity. The ion components in the TEG liquid membrane may cause a kind of facilitated transport effect on the aromatic hydrocarbon vapor.