The limiting enthalpy of solution of liquid germanium in the liquid tin ΔsolH¯Ge(l)∞ was measured at 927 K and equals 3.24 ± 0.34 kJ/mol at. The standard enthalpy of formation of intermetallic phases from the Ge-Li system were calculated at 747 K with the use of the solution calorimetric method. These alloys and intermetallic phases were prepared from pure, metallic germanium and lithium, which were melted in a glove-box filled with high purity argon with a very low concentration of impurities. The X-ray diffraction measurements were conducted to verify the structure of the prepared alloys. The electromotive force studies were performed at three temperatures: 634 K, 807 K, and 841 K by the titration technique. Based on obtained results and other thermodynamic quantities available in the literature the thermodynamic properties of phases were optimized, and the Ge-Li phase diagram was determined.