The method previously developed is applied to determine the parameters of the statistical associating fluid theory (SAFT) equation of state for amino acids. With the parameters determined, the SAFT equation of state is applied to model the amino acid solubility in water with very good precision, including L-tyrosine, L-leucine, L-aspartic acid, L-tryptophan, L-glutamic acid, L-alanine, DL-alanine, DL-valine, L-phenylalanine, DL-serine, L-proline, L-serine, and glycine. On the basis of the results of binary systems of amino acid/water, the solubility Of L-alanine and L-leucine in water at high pressures up to 3500 bar is simulated; the amino acid solubilities in an aqueous solution is modeled, including systems DL-alanine/DL-valine/H2O at 25 degrees C, DL-aIanine/DL-serine/H2O at 25 degrees C, L-glutamic acid/L-aspartic acid/H2O at 25, 40, and 60 degrees C, L-serine/L-aspartic acid/H2O at 25, 40, and 60 degrees C, and L-serine/L-glutamic acid/H2O at 25, 40, and 60 degrees C, and good agreement between modeling results and data are obtained.