The separation of Y(III) from Eu(III) using a hollow fiber-supported liquid membrane with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPNA) as an extractant was studied. The effects of HCl and metal concentrations in the feed solution, the EHPNA concentration in the membrane, and the HCl concentration in the stripping solution on the initial fluxes of the two metals and the separation factor were investigated. The optimum conditions for selective recovery of Y(III) from an equimolar solution of Y(III) and Eu(III) chlorides (0.001molL(-1) each) were as follows: HCl concentration in the feed solution, 0.1molL(-1); EHPNA dimer concentration in the organic phase in the membrane, 0.1molL(-1); and HCl concentration in the stripping solution, 4molL(-1). Under these conditions, complete Y(III) extraction was achieved after 1 ks of operation, and the Y(III) purity in the stripping solution was 84%.