The separation of nitrogen heterocyclic compounds by an (O/W)/O emulsion liquid membrane was studied. Quinoline and 2-methylnaphthalene were selected as the representative components of nitrogen heterocyclic and homocyclic compounds, and a toluene or heptane solution of these two compounds was used as the model feed oil. Deionized water or an aqueous solution of 1,3-butandiol was used as the membrane solution. Quinoline preferably permeated through the emulsion liquid membrane and could be separated from 2-methylnaphthalene in the model feed oils. The addition of 1,3-butandiol in the membrane solution could enhance the permeation rates. The separation selectivity of quinoline relative to 2-methylnaphthalene was larger with the toluene feed oil compared with the heptane solution.