The purpose of this investigation is to demonstrate that the resistance of ceramic and ceramal materials to thermal shock can he determined by analyzing the nonsteady thermal stresses in the material. First the nonuniform temperature distribution is computed by using the heat conduction equation. This temperature distribution is then used to compute the thermal stress. The material parameters which enter into the calculations are the coefficients of thermal conduction and of thermal expansion, the ultimate strength, Young's modulus, and Poisson's ratio of the material. These quantities together with the heating conditions then specify the resistance to thermal shock. The theory is verified by comparing the results with NACA test data.