The hydrolysis of methyl lactate catalyzed by an acidic cation-exchange resin, Amberlyst 15, is presented in this work. The kinetic experiments were carried out in a stirred tank batch reactor. The effects of catalyst loading, temperature, and feed composition were investigated. The reaction modeling was carried out by correlating the experimental kinetic data obtained for the esterification (previously reported) and the hydrolysis reactions simultaneously. Three models were essayed, the quasi-homogeneous, the Langmuir−Hinshelwood, and the Eley−Rideal models. Because of the high nonideality of the reaction mixture, the kinetics were expressed in terms of activities. The activity coefficients were calculated by using the group contribution method UNIFAC. The quasi-homogeneous model was found to represent the esterification and hydrolysis reactions over Amberlyst 15 fairly well.