Extraction of lanthanum, samarium and erbium into a microcapsule containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) is studied. The extraction kinetic model used to predict uptake curves is based on the interfacial reaction model accompanied by intraparticle diffusion expressed by Fick's law. The uptakes are analyzed using the kinetic model with the separately determined complex formation rate constants and the intraparticle diffusion coefficient. The rate constants used in the calculation are determined from the analysis of the kinetics data for the liquid-liquid extraction system under a low-extractant concentration. The effects of pH and metal concentration on the metal uptakes into the microcapsule are successfully predicted with the determined rate constants. From the results, it is confirmed that the extraction mechanism of metal ions into the microcapsule is same to that for a liquid-liquid extraction system. (C) 2007 Elsevier B.V. All rights reserved.