ZrB2–SiC nano-powder mixture was synthesized using ZrSi2 source material and a modified spark plasma sintering apparatus. The particle size of ZrB2 and SiC was about 80 and 20 nm, respectively. The molecular-level homogeneity of Zr/Si source and fast heating/cooling rate by SPS caused the formation of homogeneously intermixed nano-powders. A strong exothermal reaction occurred at around 860°C, which caused strong agglomeration and growth of the synthesized powder mixture. The rapid reaction could be controlled by adding 20 wt% of NaCl, which acted as an inert filler.