The vapor-liquid equilibrium (VLE) data for the quaternary system ethanenitrile + water + 1,2-ethanediol + 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) were measured at 102.5 kPa. The experimental VLE data were correlated with the nonrandom two liquid (NRTL) activity coefficient model, and the binary interaction parameters were obtained. The results show that the mixed entrainer of [EMIM]Cl and 1,2-ethanediol can eliminate the azeotropic point of ethanenitrile and water; the selectivity of [EMIM]Cl is higher than that of 1,2-ethanediol; the relative volatility of ethanenitrile to water increases with the increase of the mole fraction of mixed solvent (1,2-ethanediol + [EMIM]Cl) and the amount of [EMIM]Cl in mixed solvent, but there is no synergetic effect between 1,2-ethanediol and [EMIM]Cl. The main functions of 1,2-ethanediol are to dissolve ionic liquid and to reduce the viscosity of the entrainer. (C) 2014 Elsevier B.V. All rights reserved.