This paper reports on the development of a polymer inclusion membrane (PIM) for the selective separation of Sc (III) from other REM ions. A comparison is made of the performance of cellulose triacetate (CTA) based PIMs containing 2-thenoyltrifluoroacetone (HTTA), 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (PC-88A), N-[N, N-di(2-ethylhexyl) aminocarbonylmethyl] glycine (D2EHAG) or N-[N, N-di(2-ethylhexyl) aminocarbonylmethyl] phenylalanine (D2EHAF) as the carrier in the extraction of Sc(III) from its sulfuric acid/ammonium sulfate buffer solutions. The potential of the PIM containing D2EHAF for the selective separation of Sc(III) from a feed solution containing similar concentrations of Y(III), La(III), Nd(III), and Dy(III) into a 0.5 mol L-1 sulfuric acid receiving solution has been demonstrated. In addition, the newly developed PIM containing D2EHAF exhibited excellent stability in 5 cycles of extraction and back-extraction of Sc(III) with insignificant deterioration in its performance. The results obtained in this study indicate that the molecular structure of the carrier has a strong influence on membrane stability, and that the introduction of a phenyl group into the carrier molecule