Kinetic data on the esterification of propionic acid with n-butanol catalyzed by Amberlyst 15, Amberlyst 35, Amberlyst 39, and HZSM-5 pellets were measured at the temperatures from 353 to 383 K in a stirred batch reactor. The data indicated that the Amberlyst series resins were all effective to carry out this esterification. Because of the insignificance of the interphase and intraparticle mass-transfer resistances, a quasi-homogeneous model employing the activity of each species was used to correlate the experimental data for Amberlyst 35. A possible mechanism of this reaction was found to follow the Rideal-Eley theory in which an adsorbed and protonated propionic acid molecule reacted with an n-butanol molecule in the bulk. The activation energy of the forward reaction was found to be 14.1 kcal/mol. The activity-based equilibrium constant was found to increase slightly with an increase in temperature, indicating that this reaction is nearly isothermal.