We studied the resistance of corundum refractory during thermal-impact loadings and showed that the weakening of the material due to the action of thermal stresses may be assessed both from its residual strength and also from data for the rate of dissemination of ultrasonic oscillations and acoustic emissions, recorded during the tests. It is shown that during tests of the thermal-shock resistance of relatively brittle (χ<1) refractories they should be assessed not only with regard to the variations in temperature causing a fall in strength (as is normally done) but also with respect to the variations in temperature causing the start of microdestruction in the material.