The stability of complex compounds formed by N-phenylglycine and N-a-naphthylglycine with copper (Ⅱ) and nickel (Ⅱ) has been investigated.The stepwise formation constants of these complexes were determined potentiometrically at 25℃ in 30% ethanol solution in presence of 0.10 M sodium perchlorate.For the purpose of comparison, glycine was also investigated under the same conditions.It was found that the stability of the nickel chelates is in accord with the base strength of the amino acids, and these chelates should have tetrahedral configurations, as evidenced from magnetic susceptibility measurements.The copper complexes are normally coplanar in structure.However, copper-N-a-naphthyl-glycinate showed abnormally low stability, indicating the existence of considerable steric hindrance, which effect forced the complex to change its structure from square planar to a distorted configuration, possibly tetrahedral.