The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1 : 1 and 1 : 2 in proportion have been determined by titration calorimeter at 298. 15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1 : 2) is much less than that of the complexes (1 : 1). The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1: 1 and 1: 2 in proportion have been determined by titration calorimeter at 298. 15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1: 2) is much less than that of the complexes (1: 1).