Abstract: TiB2-TiC-SiC composite is in-situ synthesized with the use of TiH2, Si and B4C power blend under hot isostatic pressing. The fracture toughness of the fabricated composite is 7.3 MPa·m1/2. The microstructure and morphology of the composite are studied with SEM and TEM. It is shown that the grain sizes of TiB2, TiC and SiC phases are less than 10μm, and the interfaces of the three phases are clean. TiC and SiC grains are irregular polygons and TiB2grains regular platelets. The SEM analyses of the fractured surfaces suggest that transgranular fracture happened to coarse grains, and intergranular fracture to the rest of grains. Particle reinforcement, crack deflection and particle pullout are the main toughening mechanisms.