The esterification of lactic acid with ethanol was carried out in the presence of five different cation-exchange resins. The effect of catalyst type, catalyst loading, and temperature on reaction kinetics was evaluated. In order to study which components had the strongest adsorption strength on the resin surface, two simplified mechanisms based on Langmuir-Hinselwood model were compared by correlating the experimental data. FTIR method was used to verify the rationality of the mechanism. Nonideality of the liquid phase was taken into account by using activities, which were predicted by UNIFAC method instead of concentrations. The thermal stability and mechanical strength of the resin catalysts were tested by SEM. (C) 2004 Elsevier B.V. All rights reserved.