This paper reported the aggregate results and studied the complex nature of terbium (Tb), dysprosium (Dy) with mixed ligand L-aspatic (Asp) and O-phenanthroline (Phen) molar ratio 1:3:1 was isolated in solid form by the preci pitation method. By the method of elemental analysis thermal analysis and infrared spectroscopy have identified complexes is composed of Ln(Asp)3PhenCl3.3H2O (Ln: Tb, Dy). Solid complexes are unstable thermal synthesis, L-aspatic molecule associated with Ln3+ (Tb3+, Dy3+) throughnitrogen atom of the amino group-NH2 and the oxygen atoms of the carboxyl group-COO- and O-phenanthroline molecule associated with Ln3+ through atoms of the nitrogen.