The apparent acid dissociation constants of N-phenylglycine and of N-a-naphthylglycine have been determined by pH method at 250C in 30% ethanol solution in the presence of 0.10M sodium perchlorate.That of glycine was also determined under the same conditions for the purpose of comparison.These amino aeids were found to have comparable acid strengths, but their basicity is quite different.N-phenylglycine as a base is much weaker than glycine as expected, while N-a-naphthylglycine shows very strong base strength which is in the same order as that of the N-alkylglycines.This anomaly was explained in terms of steric effect due to the 8-hydrogen atom on the naphthalene ring upon the proton on the ammo group.The lowering of dielectric constant of the solvent led to the decrease of both acid and base strengths of glycine.