The scandia-zirconia (ScZ) solid solutions have been attracting attention from the communities interested in solid-oxide fuel cells because they possess the highest ionic conductivity among zirconia-based materials. However, this system shows a relatively large number of polymorphs with lack of thermodynamic data to enable comprehensive phase control for property optimization. In this work, the enthalpy of formation of the ScZ system within the range 0???20 mol% Sc2O3 is determined by combining the surface energy values with enthalpy of drop solution data obtained from high-temperature oxide melt solution calorimetry. The heats of formation, a key data for understanding phase stability, for five polymorphs: monoclinic (m), tetragonal (t), cubic (c), and rhombohedral (b and c) are reported for the first time.Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)FAPESP: 14/24022-6