The purpose of this work was to determine the thermoelectric properties of the pseudobinary system Mg2Si-Mg2Ge. The compositions investigated were Mg2Si, Mg2Ge0.2Si0.8, Mg2Ge0.4Si0.6, Mg2Ge0.6Si0.4, Mg2Ge0.8Si0.2, and Mg2Ge. X-ray diffraction lattice parameter measurements and differential thermal analysis measurements established the existence of complete solid solubility between Mg2Si and Mg2Ge. Both the lattice parameter and liquidus temperature show almost linear variation with composition in this system. The melting temperature of MgfSi was found to be 1070° ± 5°C, while that of MgfGe was found to be 1102° ± 5°. © 1963, The Electrochemical Society, Inc. All rights reserved.