High-toughness Sialon ceramic matrix composites containing alloy second-phase particles were fabricated by hot pressing at a relatively low temperature of 1600 degrees C. Substantially improved fracture toughness of 8.0 MPa.m(1/2) was achieved through the addition of varying amounts of ferro-molybdenum alloy particles. The microstructure of the composites was characterized and crack propagation behavior was observed to understand the toughening mechanisms. The results showed that crack deflection and crack bridging are the principal mechanisms in the toughening of these types of ceramic composites.