Abstract: A method based on least squares regression analysis has been proposed for the optimization of available thermodynamic properties and phase diagrams of binary systems.By using of this method, the excess entropy of binary system can be predicted from the phase diagram. Eight binary chloride systems were chosen for the study. LiCl-KCl, NaCl-SrCh, NaCl-CaCl₂, NaCl-BaCl₂, KCl-BaCl₂, CaCl₂-BaCl₂, BaCl₂-SrCl₂. The thermodynamic properties, which were expressed in mathematical form by critical analysis of all available phase diagrams and thermodynamic data, of all phases in the above binary systems have been obtained.In the same time, the phase diagram and other thermodynamic data can be critically assessed in a thermodynam.ically self-consistent manner.