The thermal diffusivities of dense polycrystalline TiB2, ZrB2, and HfB2were measured by a laser flash method over the temperature range 200°–1300°C. An investigation of the effects of radial heat flow was performed and a special sample shape was used to comply with the assumption of one‐dimensional heat flow. The values of the diffusivities were found to be described by the empirical equations&agr;TiB2=0.1290+[39.26/T(∘K)]cm2/sec&agr;ZrB2=0.1424+[81.17/T(∘K)]&agr;HfB2=0.1436+[35.97/T(∘K)].Values of thermal conductivity computed from the diffusivity data were found to be described by&lgr;TiB2=0.7867+[10.30/T(∘K)]W/cm deg&lgr;ZrB2=0.8235+[108.2/T(∘K)]&lgr;HfB2=0.7157+[34.24/T(∘K)].