The stability constants and thermodn. functions for complexes of rare earth with L-phenylalanine were determine by potentiometry and calorimetry at 25?and ionic strength of 0.15 mol/dm3 (NaCl). Stability of the complexes shows the "tetrad effect". The entropy change makes a predominant contribution to the stability of these complexes. The ligand is coordinated to rare earth ions through its-CO2- and -NH2 group, and dehydration of ions plays an important role in coordination reaction.

Key words: STABILITY CONSTANT, THERMODYNAMIC FUNCTION, RARE EARTH METAL COMPLEX, ALANINE P, CALORIMETRIC TITRATION, COORDINATION