Isobaric vapor-liquid equilibrium (VLE) data for the isopropanol (1) + water (2) system containing ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM](+)[BF4](-)) at atmospheric pressure (101.32 kPa) were measured with a modified Othmer still. The results showed that the VLE of isopropanol + water in the presence of different contents of IL was obviously different from that of the IL-free system. The IL studied showed a salting-out effect, which gave rise to a change of the relative volatility of isopropanol and even to the elimination of the azeotropic point. It was found that the salting-out effect followed the order of x(3)' = 0.30 > x(3)' = 0.20 > x(3)' = 0.10, which was probably attributed to the interaction between the ions resulting from the dissociation of IL and water.