This paper discussed the feasibility of four imidazolium-type ionic liquids (IL) as membrane materials for the separation of C-6 and C-7 aromatic/aliphatic or alicyclic hydrocarbon mixtures. Novel nanoparticle-supported membranes composed of these ILs were fabricated successfully. Liquid membranes composed of IL and aluminum oxide nanoparticles mixtures, supported by a hydrophobic porous membrane, were prepared and their efficiencies in the separation of aromatic compounds through vapor permeation were evaluated in terms of their aromatic selectivity, total permeate flux, and permeability. For an n-hexane/benzene mixture, the IL [emim][HSO4] gave the highest separation factor of 85 and the IL [emim][B(CN)(4)] showed the highest permeate flux of 0.18 kg/(m(2).h) (emim: 1-ethyl-3-methylimidazolium). Additionally, a vapor sorption test for the hydrocarbons was conducted in the ILs and sulfolane, which is a typical solvent for aromatic compounds. All the ILs showed absorption tendencies similar to that of sulfolane. The permeabilities of the ILs were 32-977 Barrer for the aromatic compounds, 0.61-186 Barrer for the alicyclic ones and 0.31-197 Barrer for the aliphatic ones. The permeabilities obtained were independent of the operating partial pressure.