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Abstract Amino acids and peptides are essential components for many industrial branches. Knowledge on the solubility behavior is required in purification processes, which often involve crystallization as main unit operation. Since the determination of experimental solubility data is expensive, thermodynamic modeling is meaningful towards reducing the experimental effort. Modeling is usually based on a solid-liquid equilibrium condition that requires the melting properties of the solids. For amino acids and peptides such data is now available, and three gE models (Wilson, NRTL, UNIQUAC) were applied in this work to model solubility in water as well as in water + 2-propanol. The new melting properties were used as input data and binary parameters for each model were fitted to experimental solubility data of the amino acids and peptides in water. Modeling solubility in water + 2-propanol required additional parameters. Binary parameters between water and 2-propanol were fitted to vapor-liquid-equilibrium data, and binary parameters between amino acid and 2-propanol as well as between peptide and 2-propanol were fitted to solubility data in water + 2-propanol mixtures. In general, the gE models allowed describing the solubility in water, while some inaccuracies were observed for the temperature dependence of the modeled solubility. Further, the decrease of solubility upon 2-propanol addition was modeled qualitatively correct using the gE models. The Wilson model was less accurate than NRTL and UNIQUAC, where the latter yielded similar results. The results were finally compared to PC-SAFT, which shows a dramatically improved modeling accuracy while using less binary parameters.