The Al2O3-ZrO2 composite ceramics were prepared by slip casting in plaster molds and sintering at 1350 degrees C in air. The composition of prepared samples varied from pure alumina to doped zirconia (3Y-TZP) with steps of 10 vol%. The relative density of the sintered samples varied from 94% to 98%, depending on the composition. Thermal diffusivity of sintered samples was measured by means of the xenon flash method at 100 degrees C, 200 degrees C, 400 degrees C, 600 degrees C, 800 degrees C, and 1000 degrees C and thermal conductivities were calculated based on measured bulk densities and specific heat data and finally corrected for porosity effects. As expected, the thermal conductivity decreased with increasing zirconia content, and in the case of samples with higher alumina content, it also decreased with increasing temperature. Effective thermal conductivities are close to the lower HashinShtrikman bound and the recently proposed sigmoidal average. Empirical relations were used to fit the dependence of effective thermal conductivity of Al2O3-ZrO2 composite ceramics on both composition and temperature.