Solid‐state phase equilibria in the MgO‐Y2O3‐ZrO2 system as well as the equilibria including liquid were investigated in the whole‐compositional range using high‐temperature differential thermal analysis (DTA), X‐ray diffraction (XRD), and scanning electron microscopy combined with energy dispersive X‐ray spectroscopy (SEM/EDX). Isothermal sections at 1493, 1573, 1693, and 1923 K were constructed based on experimental studies. The presence of tie line between MgO and Y4Zr3O12 in the temperature range between 1493 and 1573 K was confirmed. The eutectic melting in the MgO‐Y2O3‐ZrO2 system was established using DTA followed by SEM/EDX microstructure investigation. Based on the obtained experimental results, the thermodynamic database was derived.