The results of influence of amount of SiC additives to HfB₂ and the physical chemical characteristics of the additives will be under the discussion. Studies of the resistance to ablation of hot-pressed HfB₂ and HfB₂-SiC samples heated by a gas burner showed that HfB₂ ceramics with the addition of 30 wt.% SiC with average grain sizes of 30-50 μm (powder with fragmented grains with sharp edges with approximate average stoichiometry SiC_1.6O_0.1, and  6_H SiC structure) and 5-10 μm (single-crystal grains with a hypercubic shape, close to spherical, practically free of impurities, with approximate stoichiometry SiC_1.5, b-SiC) have significantly higher thermal resistance – up to temperatures of 2766 and 2780 °C, respectively (mass loss of 0.25 mg/s) than HfB₂ ceramics without additives, samples of which cracked already at 1870 °C. The formation of a framework from SiC when 40 wt.% SiC was added resulted in decrease of resistance to ablation, of Young's modulus, and the material cracking at low temperature during heating in air. The composite made from a mixture of HfB₂ - 30 wt.% b-SiC (5-10 μm) by hot pressing under a pressure of 30 MPa, 1950 °C, 30 min. with a specific gravity of 6.54 g/cm³ demonstrated the highest Vickers microhardness H_V(9.8 N)=38.6±2.5 GPa and fracture toughness, K_1c(9.8 N)=7.7 ± 0.9 MPa m^0.5, Young's modulus 510 GPa. The additions of SiC_6H with sharp fragment grains of 1 μm in size with a lamellar or strongly elongated in one direction grains, with an approximate stoichiometry of SiC_4.6O_0.75 or 3-10 μm with an approximate stoichiometry of SiC_2.3O_0.25 added in the same amount (30 wt.%) were cracked during heating in air at a temperature of 1787 and 1455 °C, respectively.