The system MgO–Al2O3was assessed with the CALPHAD technique using a computerized optimization procedure called PARROT. Two of the solid phases, MgO and spinel, showed extensive solid solubility at high temperature and were modeled with the compound energy model. The third solid phase,α‐Al2O3, was modeled as a stoichiometric phase. For the liquid phase, an ionic two‐sublattice model was used. In total, 13 adjustable parameters were optimized: 3 for the MgO, 8 for the spinel, and 2 for the liquid. This resulted in a consistent thermodynamic description for most of the available experimental data points on the phase diagram as well of the thermodynamic prop