Two ZrB2-based composites were fabricated by hot-pressing with vacuum. ZrB2+20vol%SiC and ZrB2+20vol%SiC+8vol%TiB2 were selected as the starting compositions. The microstructures and phase constitutions of the composites were investigated and compared to these of monolithic ZrB2 material. For the ZrB2-based composites, with the addition of SiC particles, the excessive growth of ZrB2 materials is restricted and grain structure is refined. Meanwhile the fracture modes are changed, namely, from transgranular to mixed inter/transgranular. Strengthening mechanism is grain refining and the toughening mechanism is crack deflection, crack branching and grain refining. The role of TiB2 as an addition to the ZrB2 matrix was also examined and discussed.