The diffusion of vacancies in the temperature gradient field is considered. As shown, the cause of thermal diffusion is an inhomogeneous temperature distribution in the medium, which leads to spatial asymmetry of the activation process of atom transfer and causes a diffusion flux of atoms directed along the temperature gradient. The equation of thermal diffusion of vacancies in a medium is obtained, the solution of which is given in the case of a stationary temperature gradient. As shown, the appearance of a temperature gradient in the crystal leads to the movement of vacancies from the cold to the hot region of the crystal and in some cases, leads to the vacancies outflow from a crystal bulk.