Aluminum oxide has been introduced into SiCf/(SiC + B4C) composites to improve the crack self-healing property in O-2/H2O atmosphere. The observation of the surface and interior morphologies of the oxidized composites reveal that Al(2)O(3)can lead to rapid self-healing of cracks, which will effectively block the oxidation of interior interphase and fiber. Further investigation reveals that Al(2)O(3)plays an important role in impeding the crystallization of SiO(2)and limiting the volatilization of B2O3. It is beneficial to form self-healing fluid glass phase and improve glass phase stability. Under these circumstances, the pre-crack can be healed more effectively, which is advantageous for composites to remain high strength retention rate.