It is known that SiC whisker/Al2O3 matrix composites can oxidize in air at high temperature and then form oxidation layers on their surfaces. Oxidation treatment has been experimentally performed in air at 1450-degrees-C for a pre-determined time. The results show that the surface layer is in a state of compressive residual stress. The oxidized specimens have better resistance to thermal shock damage than the non-oxidized specimens. However, the surface oxidation can degrade the room-temperature flexural strength.