High-pressure sintering the pure phase B6O is investigated using in-laboratory-synthesized B6O. Sintering behavior of three different grain sizes B6O powder ( 20-40nm, 0.2-1um, or 1-5 um) under the high-pressure (5–20 GPa) and high- temperature (1500°–2000°C) conditions that have been investigated.  Sintered B6O bulk of almost-full density were prepared by sintering at a pressure of 15 GPa and temperature of 2000°C for 10 min. The maximum Vickers microhardness (34 GPa) of sintered B6O bulks was attained. the maximum fracture toughness (2.1 MPa∙m 1/2) was observed.