Yb∶YAG laser crystals are grown by the Czochralski technique. The specific heat and thermal diffusivity data of Yb∶YAG are measured. It shows that the doping of Yb 3+ ions leads to the decrease of specific heat and thermal diffusivity, especially when the doping concentration is high. And the decrease of the latter is regard as the result of lattice deformation caused by the doped Yb 3+ ions.