A new extraction agent, N-pentafluorobenzoyl-N-phenylhydroxylamine (PFBPHA), was synthesized. The solvent extraction of Pr (II), Eu (II) and Yb (II) with PFBPHA has been investigated at an ionic strength of 0.2 and 25 ±1°C It. The acid dissociation constant, KD, and the partition coefficient, KD, of its metal complexes were determined. These results obtained were compared with those of N-benzoyl-N-phenylhydroxy1amine (BPHA) reported previously. The introduction of fluoro group to the C-phenyl ring of BPHA was very effective for increasing not only the Kavalue of PFBPHA but also its KDvalue and the extraction constant, KBX, of its lanthanoid complexes.