Isobaric vapor-liquid equilibrium (VLE) data for the acetonitrile + water system containing ionic liquids (ILs) at atmospheric pressure (101.3 kPa) were measured. The ionic liquids investigated were 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim] [BF4]), 1-butyl-3-methylimidazolium dibutyl phosphate ([Bmim][DBP]), and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]). The results showed that [Bmim][BF4] was ineffective to the enhancement of relative volatility of the acetonitrile + water system. [Bmim] [DBP] and [Bmim][Cl] could increase the relative volatility of acetonitrile in the whole concentration range and eliminate the azeotropic point. The separation ability of ILs was [Bmim] [Cl] > [Bmim][DBP]. VLE data for the acetonitrile + water + IL systems were correlated by the nonrandom two-liquid (NRTL) model. The NRTL model was applicable to the correlation of ILs containing systems with the average deviation being 5.17 %.