Communication: The tremendous enhancement of the physical, chemical, and mechanical properties of materials in their nanocrystalline state is being exploited in a number of frontier technologies; however, concern in the use of nanocrystalline materials is their stability during high-temperature exposure, either while processing or in service. Reported in this communication is a new solid-state electrochemical method for the accurate determination of high-temperature surface thermodynamic properties of nanocrystalline ceramics, using MgAl2O4 as a model compound.