Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L-1)-(L-10) of General formula [Ln(L)(NO3)(2)(H2O)(2)]NO3 have been synthesized. These complexes have been characterized by analytical, spectral and thermal studies. Molar conductance data show that these complexes are 1: 1 electrolytes. The presence of two coordinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones, in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (beta), covalency factor (b(1/2)) and Sinha's parameter (delta) evaluated from electronic spectral data of dysprosium(111) complexes indicate a little covalency in metal-ligand bonding.