The solvent extraction of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from weak acidic chloride solutions into an organic phase containing 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (HP) and phosphoryl-containing podands (L) has been studied. A considerable synergistic effect was observed in the presence of neutral ligands L in the organic phase containing HP. The stoichiometry of the Ln(III) extracted species was determined by slope analysis and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted with mixtures of HP and neutral ligands in toluene from weak acidic solutions as LnLP3 complexes.