Isobaric vapor-liquid equilibrium data for the ternary systems of methanol + methyl ethyl ketone (MEK) + 1-buty1-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and methanol + MEK + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonypimide ([HMIM][NTf2]) have been measured at 101.3 kPa using a modified Othmer still. The data obtained were correlated using NRTL model and fitted in well with it. The results showed that the addition of ionic liquids (ILs) into the azeotropic system caused a significant salting-in effect on MEK, thus increased the relative volatility of methanol to MEK and broke the azeotrope. And [HMIM][NTf2] has a stronger effect than [BMIM][NTf2]. The elimination of azeotropic phenomenon could be achieved when the mole fraction of ILs in the liquid phase was 0.05 (about 0.40 in mass fraction) or more. The effect of the ILs in this study was compared with that of some other ILs. (C) 2016 Elsevier B.V. All rights reserved.