The extraction of Zn2+ and Cu2+ from binary solutions in a microporous hollow fiber with di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene was examined. Experiments were performed at different metal concentrations (3.13-15.7 mol/m(3)), metal concentration ratios (0.25-4), pH (3-5), and D2EHPA concentrations (50-200 mol/m(3)). A mass transfer model was presented that considers diffusion in the aqueous layer, membrane, and organic layer. On the basis of the knowledge of extraction chemistry and transport properties of the relevant geometry, the validity of the model was checked from time changes of aqueous metal concentrations in the single systems (standard deviation, 9%). For binary systems, comparisons of the experimental data and the calculated results which directly taking the model parameters obtained in the single systems revealed that a synergistic effect on Zn2+ extraction occurred at the latter stage of the processes.