Boron carbide (B4C) has attractive properties such as high melting point, low density, high hardness, high neutron absorption capability, chemical stability and good impact and wear resistance. Due to these unique properties, it finds wide range of applications in industrial cutting-grinding tools, nuclear reactors, wear resistant components, abrasive materials and lightweight armors. However, it has limited sinterability at low temperatures without use of additives. Zirconium diboride (ZrB2) is a promising additive to overcome the low sintering ability of B4C and also to promote its mechanical properties. In this study, B4C-ZrB2 composites with the varying amounts of ZrB2 (0, 5, 10, 15, 20 vol. %) were prepared by spark plasma sintering at 1650°C in vacuum environment. The effects of ZrB2 content and sintering temperature on the densification, hardness, fracture toughness and microstructure will be investigated.