Si3N4-barium aluminum silicate (BAS) self-reinforced composites have been prepared by pressureless sintering at 1800 A degrees C for 2 h. The beta-Si3N4 seeds incorporated in the starting alpha-Si3N4 powders encouraged the alpha- to beta-Si3N4 phase transformation, and the final bimodal microstructure with large grains, consequently, led to the improvement of the fracture toughness, from 7.74 to 8.34 MPa m(1/2). The almost-complete crystallized BAS benefited the high-temperature mechanical properties. The residual stress, crack deflection, grain bridging, and pullout were considered as the major toughening mechanisms in this composite.