An extraction resin, with styrene-divinyl benzene copolymer as the supporter and 2-ethylhexyl phosphonic acid mono-2-ethyjhexyl ester (HEH[EHP]) as the extractant, was synthesized by suspension polymerization, and its performance in separating rare earths, such as gadolinium and terbium, was investigated. Especially, the effect of the stirring speed and the ratio of porogenic-agents in synthesizing the resin were examined. It was concluded that the optimal condition for synthesizing the resin is a stirring speed of 3000 rpm with a 10/10 wt.% ratio of toluene/n-heptane as the porogenic-agents. It was determined that the porogenic-agent could only increase the surface area of extraction resin and did not influence the particle size. Synthesis under these conditions will yield 0.628 g HEH[EHP]/g resin, with a resolution value,alpha(Gd)(Tb) of 0.727 and longest effluent ranges of 675 ml. The extracted Gd and Tb were both 99.9% pure. (C) 2004 Elsevier B.V. All rights reserved.