The addition of Ti 3 SiC 2 particles can enhance the toughness of Al 2 O 3 . The toughening mechanism for the Al 2 O 3 /Ti 3 SiC 2 composites is investigated in the present study. Though the Ti 3 SiC 2 particles are constrained by the rigid Al 2 O 3 matrix, crack deflection can still take place within the Ti 3 SiC 2 particles. The toughening effect is mainly contributed by such crack deflection. The experimental results match well with the theoretical prediction. However, in order to allow the crack deflection to take place within Ti 3 SiC 2 particle, the pre-existence of plastic deformation within the particle is essential. The interactions between crack deflection and plastic deformation are discussed.