A novel microstructure of in situ produced TiC/TiB2/MoSi2 composite and its mechanical properties were investigated. The results indicate that TiC/TiB2/MoSi2 composites can be fabricated by reactive hot pressing the mixed powders of MoSi2, B4C, and Ti. A novel microstructure consisting of hollow particles of TiC and TiB2 grains in an MoSi2 matrix was obtained. Grains of in situ produced TiC and TiB2 were much finer, from 100 to 400 nm. During the fracture process, hollow particles relieved crack tip stress, encouraging crack branching and changing the original direction of the main crack. The highest bending strength of this composite achieved was 480 MPa, twice that of monolithic MoSi2, and the greatest fracture toughness of the composite reached 5.2 MPa center dot m(1/2).