Heteropoly-complexes K17[Ln(CuW11O39)2].xH2O(Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy) were prepared. The properties of the products were investigated by ion-exchange, conductometric titration, IR, UV and X-ray powder diffraction. The results show that the structure of the products is similar to that of U(a-Ge11O39)2 and consistent with the model proposed by Peacock. Heteropoly-complexes K17 [Ln (CuW11O39) 2] .xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy) were prepared. The properties of the products were investigated by ion-exchange, conductometric titration, IR, UV and X-ray powder diffraction. The results show that the structure of the products is similar to that of U (a-Ge11O39) 2 and consistent with the model proposed by Peacock.