The solubilities of five cyclic dipeptides : c-(glycylglycine), c-(L-alanylglycine), c-(L-alanyl-L-alanine), c-(L-valyl-L-valine), and c-(glycyl-L-leucine), in water at the temperature 298.15 K have been redetermined using an improved technique. The solubility constants of the dipeptides were used to calculate molar Gibbs free energies of dissolution. Also, the molar enthalpies of dissolution and the corresponding heat-capacity changes previously determined in our laboratory were re-evaluated from the new solubility constants. Finally, from the molar enthalpies and the Gibbs free energies of dissolution, the corresponding molar entropies of dissolution of the dipeptides were calculated.