Coatings of zirconia alloyed with 25wt% ceria and 2.5wt% yttria or 8wt% yttria were prepared using the air plasma spray(APS) process. For each of these coatings thermal shock resistance and thermal expansion parallel to the substrate under the 1300℃ high temperature environment were measured to investigate the phase transformation behavior of ceramic top coating and thermal expansion mismatch stress. Microhardness test was also used to compare ZrO₂-25CeO₂-2.5Y₂O₃ with ZrO₂-8Y₂O₃ coating in the light of mechanical property. These results were discussed in conjunction with the phase stability of the specimens, as determined by X-ray diffraction. The ZrO₂-CeO₂-Y₂O₃ coating was found to have more stable thermal properties than ZrO₂-Y₂O₃ coating. The thermal shocked ZrO₂-Y₂O₃ coating exhibited a non-linear thermal expansion curve which was probably due to a reversible tetragonal-monoclinic transformation.