We have synthesized a family of new extractants, alkyl phenylphosphonic acids, for strontium removal by supported liquid membranes (SLMs) with strip dispersion. The stability of the SLMs has been ensured by the improved SLM with strip dispersion technique. The SLMs removed radioactive Sr-90 to the target of 8 pCi/L or lower from feed solutions of 300- 1000 pCi/L. Overall mass transfer coefficient data indicate that the mass transfer resistance for the membrane phase is negligible. An analysis of mass transfer resistances shows that the interfacial resistances due to extraction and stripping reactions are dominant. Stripping with HCl was nearly quantitative and more effective than that with H2SO4. The extractant was more effective than di(2-ethylhexyl) phosphoric acid.