The removal and recycling of acetic acid from acetic acid + water mixture has a great significance for environmental protection and resource utilization. After the addition of ionic liquid (IL) 1-butyl-3-methylimidazolium dibutylphosphate [BMIM][DBP], the boiling point difference of the water + acetic acid system increased from 17.88 K (0 mass % IL) to 41.13 K (about 59 mass % IL), and the relative volatility (x(1)' = 0.9) increased from 1.60 (0 mass % IL) to 9.81 (about 57 mass % IL). [BMIM][DBP] showed a remarkable entrainer performance for the separation of acetic acid from aqueous solution. In this work, Isobaric vapor-liquid equilibrium (VLE) data of the systems water + acetic acid, water + [BMIM][DBP], acetic acid + [BMIM][DBP], and water + acetic acid + [BMIM][DBP] were determined at 101.32 kPa by using an improved Rose-Williams equilibrium still. Based on the chemical theory and Hayden-O'Connell (HOC) method, the parameters of NRTL model for the binary systems were obtained, and the predicted values of the ternary systems of water + acetic acid + [BMIM][DBP] fitted the experimental VLE data well. (C) 2013 Elsevier B.V. All rights reserved.