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ZrB 2 -SiC powders with different amounts of SiC (10–30 wt%) were in-situ synthesized at 1600 °C for 90 min in Ar atmosphere. Effects of SiC addition on the formation of ZrB 2 via carbothermal reduction of ZrO 2 , H 3 BO 3 and carbon black were investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The grain size of ZrB 2 in final powders decreased with adding SiC. Columnar ZrB 2 and granular SiC were combined interactively when the SiC content was 25 wt%. Layer-like hexagonal SiC was obtained in the product containing 30 wt% SiC, whereas the ZrB 2 grain growth was strongly inhibited. Furthermore, the growth mechanisms of ZrB 2 and SiC were studied. [ABSTRACT FROM AUTHOR]