Abstract: The apparent acid dissociation constants of N-α-naphthylglycine and N-β-naphthylglycine and the stability constants of their complex compounds formed with copper(Ⅱ) and nickel(Ⅱ) have been determined by pHmethod at 25.0℃ in 20%(V/V), 50%(V/V) and 75%(V/V) dioxane-water mixed solvents in presence of 0.10 Msodium perchlorate. The data obtained in 20%(V/V) dioxane-water were compared with those in 30%(V /V) ethanol solution and the solvent effect upon the stability of these complex compounds was discussed. It was found that, under the same conditions, even though N-α-naphthylglycine showed higher basic and lower acidic strength than its isomer N-β-naphthylglycine, it showed, however, lower stability. This fact infers considerable steric effect existing in the molecule of the former complex compound and a modification of configuration is implied.