The solubilities of the tertiary mixtures L-alanine/L-leucine, L-alanine/L-valine, and L-leucine/L-valine in water were measured at 303 and 323 K. The Solubilities of seven binary, eight tertiary, and one quaternary amino-acid systems were modeled using the PC-SAFT equation of state. For this Purpose, new parameters for L-aspartic acid, L-glutamic acid, L-leucine, and L-tyrosine are presented. The model excellently reproduces binary solubility data with a linear temperature-dependent binary interaction Parameter for the solute-solvent interaction. PC-SAFT allows for a very good prediction of the Solubility behavior of ternary mixtures over a wide range of temperature and concentration. The aqueous mixture With three amino acids is then predicted without any further adjustment with all average relative deviation of 3.34%.