The kinetics of alkaline hydrolyses of nine amino acid esters by the process H,2NCHRCO2R'+OH- + H2NCHRCO2-+R'OH have been studied at 25º and an ionic strength of 0.1M in water over a range of pH. The acid ionization constants of the various amino acid esters have been determined, and these are roughly 2 pK units lower than those of the corresponding amino acids. The kinetic measurements are interpretable on the basis of electrostatic and steric effects.