The vapor-liquid equilibrium (VLE) data for the ternary systems of tetrahydrofuran (THF) (1) + methanol (2) + 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) (3) and THF (1) + methanol (2) + 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) (3) are measured at 101.3 kPa with a modified Othmer still. The ionic liquids (ILs) give rise to the relative volatility of THF to methanol. [EMIM][BE4] has a stronger effect on the enhancement of the relative volatility than [BMIM][BF4]. [EMIM][BF4] even eliminates the azeotropic point when its mole fraction is up to 0.20, whereas [BMIM][[BF4] pulls down the azeotropic point. The effect of two ILs on the VLE for THF+ methanol system is discussed. The NRTL model proposed by Renon and Prausnitz reproduces the experimental values well. (C) 2013 Elsevier B.V. All rights reserved.