Hot-pressed composite ceramics with 0-30 vol% SiCw have been investigated to determine the effect of composition (i.e., amount of SiC whiskers) on the microstructure and mechanical properties. The composites exhibited superior mechanical properties, especially in fracture toughness, compared to monolithic TiB2. Fracture toughness measured by the single-edge notched beam method increased from 3.4 MPa root m for the hot-pressed unreinforced TiB2 to 7.8 MPa root m for the composite containing 30 vol% SiC whiskers. The lack of increase in flexural strength of the composites with increasing volume fraction of SiC whisker can be explained by a decrease in relative density associated with SiCw agglomerates. Finite element method analysis and scanning electron microscopy observation show that the toughening mechanisms may be attributed to crack deflection around whiskers and whisker bridging due to whisker pullout.