Rates and mechanism of the liquid-liquid extraction of lactic acid from aqueous solution with tri-n-octylamine in xylene were studied using a microporous membrane-based stirred cell. It was shown that this operation could give intrinsic rate equations for the formation and dissociation of the acid-amine complexes. A possible reaction mechanism was also proposed. In addition, the effect of temperature on the reaction rates was studied and the activation energies were obtained. Finally, the results of transport parameters and reaction kinetics indicated this extraction process (either forward or backward) to be predominantly controlled by interfacial chemical reactions, under the conditions investigated.