There　is　a　reversible　reaction　(sec-butyl　acetate + water　⇔　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.　©　2016　Elsevier　B.V.