The thermal shock behavior of isotropic and anisotropic porous Si3N4 was evaluated using the water-quenching technique. The critical temperature difference for crack initiation was found to be strongly dependent on the ratio of fracture strength to elastic modulus. Because of a very high strain-to-failure, anisotropic porous SO, showed no macroscopic cracks and was able to retain its strength even at a quenching-temperature difference of similar to 1400degreesC.