The ZrB2- and HfB2-based materials are promising for application in hypersonic aerospace and atmospheric re-entry vehicles, cutting tools, metallurgy, microelectronics and refractory industries in general. The structure and properties of sintered under high pressure (4GPa) – high temperature (1800 oС) conditions ZrB2, HfB2, ZrB2+30%TiB2 and ZrB2-20% SiC refractory materials are under consideration. High-pressure sintered HfB2 (a=0.3141, c=0.3473 nm γ=10.42 g/cm3) demonstrated hardness HV(9.8 N)=21.27±0.84 GPa, HV(49 N)=19.29±1.34 GPa, and HV(98 N)=19.17±0.5 GPa and fracture toughness K1C(9.8 N)=6.47 MNm0.5. According to literature data HfB2 which demonstrated the same density, but obtained by spark plasma sintering (SPS) at 50 MPa and 1300 oC, had lower hardness: HV(9.8 N)= 19.8±0.7 GPa. High pressure sintered ZrB2 (a=0.3167 , c=0.3528 nm, γ=6.1 g/cm3) demonstrated HV(9.8N)= 17.66±0.60 GPa, HV(49 N)= 15.25±1.22 GPa, and HV(98 N)= 15.32±0.36 GPa and K1C(9.8 N)=3.64 MNm0.5. Addition of 30 wt.% of TiB2 to ZrB2 and high pressure sintering at 1800 oC leaded to formation of the structure having density γ=5.29 g/cm3 which contained ZrB2- 56 wt.%, TiB2-22 wt.% and solid solutions (Zr,Ti)B2-4 wt.%, (Ti,Zr)B2-18 wt.%. But the addition of TiB2 and sintering at 1800 oC under 4 GPa did not allow to increase hardness of the material essentially (HV(9.8 N)=17.75±2.36 GPa). One can conclude that sintering temperature increase under high pressure conditions may bring to improvement of mechanical characteristics of ZrB2-TiB2 composite material. Addition of 20 wt.% of SiC to ZrB2 and sintering under high pressure allowed essential increase of hardness to HV(9.8 N)=24.18±0.7 GPa, HV(49 N)=16.68±0.5 GPa, and HV(98 N)=17.59±0.4 GPa and fracture toughness (K1C(9.8 N)=6.49 ± 0.25 MNxm0.5, K1C(49 N)=7.06± 1.55 MNm0.5 , K1C(98 N)=6.18± 1.24 MN•m0.5) of composite ZrB2- SiC material (with γ=5.03 g/cm3). Projects NATO SPS G5773; 03-03-20, ISM-29/20, III-3-20 (0779), of NASU.