The sorption and transport of amino acids such as glycine, L-valine and L-leucine through charged polysulfone membranes was investigated as a function of pH lower than 5.6 under three different interfacial conditions. The sorption was characterized by the Langmuir and the Freundlich equations. The highest permeability was obtained if the initial pH on the amino acid source side was 5.6 and that on the opposite side 2.5, the intermediate permeability was obtained if the initial pH on both sides was 2.5, and the smallest permeability was obtained if the initial pH on the amino acid side was 5.6. The obtained results are explained in terms of the interfacial transport based on the chemical reaction (protonation and ion exchange).