An apparatus for the thermal diffusivity measurement of refractory solids at high temperatures (800–1800 K) by the periodic stationary method is presented. A cylindrical geometry for the sample has been chosen. The radial heat flow through the measurement cell is sine modulated and induces a thermal sine wave over the lateral side of the sample. The thermal diffusivity is determined from the measurement of the phase change and the amplitude ratio between two points of the sample. Thus, the thermal diffusivity can be obtained in two manners. The difference between these results is a criterium for the validity of the measurement. Experimental results on a sample of a cordierite based sintered material (Cecorite 130P) are presented. They show good agreement with the results of the CODATA Task Group on Thermophysical Properties.