AbstractYttria‐stabilized zirconia has been studied as a candidate standard reference material for the determination of thermal properties. This study evaluated the high‐temperature stability, which is important for yttria‐stabilized zirconia to be used for a standard reference material, using a common material of fine ceramics, Referceram ZR1 (zirconia). The high‐temperature stability was evaluated by measuring the change in the thermal diffusivity before and after heat treatment at temperatures between 200 °C and 1500 °C. No change in the thermal diffusivity was observed when the samples were treated at temperatures equal to or below 900 °C. However, it was revealed that the changes in the thermal diffusivity were caused by the transformation and separation of the crystal phase and the cracks that occur at grain boundaries when the samples were treated at temperatures equal to or above 1000 °C. From these results, we confirmed that Referceram ZR1 is sufficiently stable for use as a reference material at temperatures equal to or below 900 °C. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(2): 57–67, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20193