The results of calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system are presented in this article. The research was carried out experimentally, using Oelsen calorimetry in temperature interval 800–1,000 K, and by thermodynamic calculation, applying general solution model in temperature interval 800–1,600 K. The enthalpy space diagram, the enthalpy isotherm diagram, as well as the values for zinc activities, partial and integral molar Gibbs excess energies have been determined. Comparison of experimentally obtained results and the results calculated by general solution model was done at the temperatures 800, 900, and 1000 K, which indicated a good mutual agreement.