The esterification reaction of acetic acid and alcohol is one of the processes applying reactive distillation technology. It is known that the thermodynamic properties are essential to chemical process design. In this study, the thermodynamic behaviors of vapor-liquid equilibrium (VLE) and reaction equilibrium of acetic acid, I-pentanol, n-amyl acetate, and water mixture were determined experimentally. Since the present esterification reaction is very slow, thus, a sulfuric-aluminum oxide catalyst prepared in our laboratory was used to accelerate reaction rate such that the chemical reaction equilibrium will be reached ahead of phase equilibrium. Then this complicated problem was simplified and readily to be solved. The reaction equilibrium constants at different temperatures were calculated with experimental VLE data and the reaction and phase equilibrium equations. We found that the reaction equilibrium constant was slightly dependent on temperature. The experimental VLE data were correlated by the models of UNIQUAC and NRTL with the consideration of vapor molecular association of acetic acid. Figures showing the experimental data and the calculated composition surfaces were plotted against temperature. From these figures, we observed that reactive azeotropy as described by Barbosa and Doherty [D. Barbosa, M.F. Doherty, 1987. Proc. R. Sec. London Ser. A, 413, 443-459.] does not exist for this quaternary mixture.