There is a reversible reaction (sec-butyl acetate + water double left right arrow sec-butyl alcohol + acetic acid) catalyzed by acetic acid in the quaternary system water + sec-butyl alcohol + sec-butyl acetate + acetic acid. In this work, the liquid-liquid equilibrium (LLE) data for this quaternary system were determined at 303.15-333.15 K at atmosphere pressure. The LLE model of this quaternary reaction system was established with consideration of the chemical equilibrium of the reversible reaction. The measured LLE data were used to correlate the binary interaction parameters of the NRTL and UNIQUAC models. The NRTL model is more suitable than UNIQUAC model for describing the LLE of this quaternary reaction system. (C) 2016 Elsevier B.V. All rights reserved.