The ternary system ZrO₂–MgO–Al₂O₃ as a whole has not yet been studied. Literature data are available only for the binary systems that form the sides of this ternary system. A study of melting temperatures was carried out along three sections in the ternary system ZrO₂–MgO–Al₂O₃, and it was found that in the direction from ZrO₂ to the chemical compound MgO·Al₂O₃, there exists a continuous region of solid solutions whose melting point increases with increasing ZrO₂ content from 2130°C (spinel) to 2715°C (ZrO₂). The absence of a eutectic, which would cause premature softening of the material, makes these mixtures very important as highly refractory materials.