We present a series of experiments especially designed to show the effects of pH on the interfacial transport of glycine through a cation exchange membrane. The experimental results are explained qualitatively by using a theoretical model which incorporates the equilibrium dissociation equations for the fraction of amino acid forms at different pH values, a rate equation for the membrane interfacial transport based on the interfacial chemical reaction, and the Nernst-Planck flux equations for the ion transport through the bulk of the membrane. The results appear to indicate that the rate-limiting step in the amino acid transport process could be the rate at which glycine exits the membrane, and they contribute to a better understanding of amino acid permeation across charged membranes.