A thermodynamic assessment of the quasi‐binary system CaO‐Al2O3has been made using a computerized CALPHAD (calculation of phase diagrams) technique. The actual optimization was carried out with a computer program for the optimization of parameters in thermodynamic models called PARROT. The liquid phase is described by a simple two‐sublattice subregular solution model with Ca2+and Al3+as cationic species and O2‐as anionic species. All solid phases are treated as stoichiometric compounds. A consistent set of parameters describing the system is presented, and numerous comparisons with experimental data are made. There is a lack of accurate data in the high‐alumina part of the system, and the importance of a better knowledge of the CaO·6Al2O3phase i