<p>Due to the positive effects of Si, graphite, and silicon carbide on sinterability, they were selected as additives, and their effects on the microstructure and mechanical properties of (HfTaZrTiV)C high-entropy ceramic were investigated. For this purpose, (HfTaZrTiV)C ceramics without additives (HZTTV) and with graphite and Si additives (HZTTV/SiGr) were sintered by the spark plasma sintering (SPS) method at 2000°C. The relative density of the samples was measured by the Archimedes method. Phase identification was done using X-ray diffraction analysis (XRD). Microstructural studies and elemental distribution analysis were carried out using field-emission scanning electron microscopy (FE-SEM) and energy-dispersive spectroscopy (EDS), respectively. The XRD results showed that a solid solution formed in both samples. Also, the grain size measurement showed that both samples have submicron grain sizes of 0.73 ± 0.2 and 0.76 ± 0.3 for HZTTV/SiGr and HZTTV, respectively. In the HZTTV/SiGr sample, the relative density, hardness, and fracture toughness are significantly higher than those of the HZTTV sample, reaching 99.7%, 32.5 GPa, and 5.8&#xa0;MPa m^0.5 from 95.8%, 21.5 GPa, and 4.3&#xa0;MPa m^0.5, respectively. The dominant toughening mechanisms in HZTTV/SiGr were crack deflection and crack branching.</p>