Abstract: No experimental therniodynamic properties of Ge-Si system have been reported in literature. But the phase diagram has been measured exactly many times. In this paper the thermody namic properties of Ge-Si system have been calculated from phase diagram by using computer program CABPD (Calculating Activities from Binary Phase Diagrams) presented by the author in a previous paper. The excess free energies in liquid and solid solution can be expressed as:
E_Gm(L)=7125X_SiX_Ge(J/mol)
E_Gm(S)=4808X_SiX_Ge(J/mol)
and the activities of Ge and Si in liquid and solid solution have been also given. They show positive deviations from Raoult's law.