The binary systems ZrO 2 -YO 1.5 , ZrO 2 -TiO 2 , and YO 1.5 -TiO 2 are reassessed, and a set of self-consistent thermodynamic parameters, which can be reliably extrapolated into the ZrO 2 -YO 1.5 -TiO 2 ternary system, are obtained. The substitutional solution model and the stoichiometric compound model are applied to the phase description in the ternary system, and the thermodynamic database of this ternary system is derived by the CALPHAD approach. It is noted that, except for the liquid phase, no ternary interaction parameters are introduced. The present evaluation can better describe the experimental phase diagrams reported recently at 1573 K, 1773 K, and 1873 K (1300°C, 1500°C, and 1600°C). Thus, the optimized thermodynamic parameters may be authentic and can be applied to optimizing the compositions of the novel materials based on this ternary system.