The results of investigation of the temperature fields arising in the process of cutting of crystalline materials are presented. The temperature distributions in the cutting zone and in the neighboring regions were determined with the use of an infrared thermograph. It is shown that, in the process of cutting of sapphire, the temperature reaches a maximum at a certain distance before the cutting zone. With time the temperature of the sapphire increases monotonically or passes through a maximum depending of the load applied. The kinetic dependence of the temperature of diamond also passes through a maximum. It has been established that the temperature of diamond crystal subjected to cutting under hard conditions increases markedly, which can lead to the separation of large parts, probably because of the growth of fatigue cracks due to the intense heating of the material.