(Liquid + liquid) equilibrium (LLE) data of the (water + acetic acid + dibutyl phthalate) system have been determined experimentally at T = (298.2, 308.2, and 318.2) K. The reliability of the experimental tie lines data was ascertained by using the Othmer-Tobias correlation. The UNIFAC model was used to predict the phase equilibrium in the system using the interaction parameters between AC, ACH, CH2, CH3, CH2COO, COOH, and H2O functional groups. The experimental data were compared with predicted by UNIFAC model. Distribution coefficients and separation factors were evaluated for the immiscibility region. (c) 2005 Elsevier Ltd. All rights reserved.