The mechanical properties of a commercial polycrystalline yttria partially stabilized zirconia (Y-PSZ) are evaluated as a function of temperature up to the onset of creep. Hertzian indentation tests in combination with finite element modeling (FEM) are used to determine its elastic-plastic properties up to 1000 degrees C. Vickers hardness measurements are also performed at selected temperatures to complement the mechanical characterization. In addition, critical loads for radial and ring crack initiation are determined from postmortem inspection of test surfaces. The results reveal a dramatic hardening and strengthening of Y-PSZ as the temperature decreases below 600 degrees C, effects that are attributed to the tetragonal-to-monoclinic (t -> m) transformation. Above the transformation temperature, the material strength continues to decrease with increasing temperature but at a lower rate, an effect that is explained by a gradual grain boundary degradation.