This work studied the separation effect of 1-hexyl-3-methylimidazolium-based ionic liquids (1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM] [BF4] and 1-hexyl-3-methylimidazolium trifluoromethanesulfonate [HMIM][OTF]) to separate a methanol and acetonitrile azeotropic system. The isobaric vapor-liquid equilibrium data obtained for the ternary systems {methanol + acetonitrile + ([HMIM][BF4] or [HMIM][OTF])} were measured at 101.3 kPa. Based on the nonrandom two-liquid model, the minimum mole fractions of [HMIM][BF4] and [HMIM][OTF] required to eliminate the azeotrope point of the methanol + acetonitrile mixtures were 0.047 and 0.042, respectively. Through the analysis of the sigma-profiles and separation ability, [HMIM] [OTF] was a suitable entrainer to separate the methanol-acetonitrile azeotrope.