Abstract: In this paper protonation constants of the title ligands at various temperatures as well as stability constants(K₁, K₂) of its chelates with rare earth elements in H₂O and in mixed solvents were determined potentiometrically at 30℃ and at ionic strength of 0.10. The calculations of these constants were carried out by different methods on DJS-131 electronic computer, the data have been also treated by a least-squares method. Two important facts can be observed from the results obtained. First, there is an apparent "tetrad effect" in both systems. The second fact to observe is the shift of the y position from its usual Ho-Er region to the vicinity of Gd (for aspartic) and Nd (for asparagine system). It can be reasonably explained by the different polarizability between the lanthanides and yttrium ion.