γ-Zirconium phosphate-phosphite, γ-Zr·PO4·H2PO3·2H2O, (γ-ZrPP), was prepared and characterized. Direct treatment of γ-zirconium phosphate-phosphite with an ethanol solution of 0.1M 1,10-phenanthrolin and 2,2'-bipyridyl gave the well defined composites, γ-Zr·PO4·H2PO3(phen)0.15·H2O and γ-Zr·PO4·H2PO3(bipy)0.18·0.6H2O respectively.K d values of a mixture of lanthanide ions: La3+, Sm3+, Eu3+ and Yb3+ for the intercalated products and for γ-ZrPP in HNO3 solution at room temperature and at pH 2 and 4 were determined by a radiotracer technique.140La,152mEu,153Sm and175Yb radioisotopes were used for the equilibration experiment using 500 μl (4.0·10−5 mmole) each of the solutions of the tracers as a mixture in 7.5 M HNO3 solution at the desired pH with 0.1 g of γ-ZrPP and of the intercalated products. The selectivity order was found to be dependent on the nature of the ligand and on the pH. The 2,2'-bipyridyl product posseses, at pH 2 in general, a highK d value, specially for Sm3+ (9815.9) compared to that of the 1,10-phenanthrolin product (3375.5) and to γ-ZrPP (419.8). This could be attributed to partial deintercalation of the 2,2'-bipyridyl at pH 2 and increasing of ionogenic groups.