- The effect of boron carbide composition on its sintering behavior was investigated. Boron carbide of various compositions was synthesized by reacting stoichiometric boron carbide with TiO 2 . Titanium oxide was reduced by carbon that originated in stoichiometric boron carbide, leads to a decrease its carbon content and the formation of TiB 2 phase. Powder mixtures containing boron carbide of various boron to carbon ratios ( x in B x C was changed from 4.05 to 6.33) and different vol% of TiB 2 (from 6 to 21 vol%) were synthesized and densified by spark plasma sintering at 1800 and 1900 °C under an uniaxial pressure 50 MPa for 30 min. A mixture of stoichiometric boron carbide with 20 vol% TiB 2 was densified under the same conditions. The positive effect of boron carbide composition on the sintering behavior was clearly observed, while only minor effects of TiB 2 addition were detected. It was established that the carbon concentration in boron carbide gradually decreased in the 1200–1700 °C temperature range during spark plasma sintering and after sintering at 1800 and 1900 °C when the B to C ratio ( x ) was already close to its stoichiometric value, regardless of the initial carbon content. Mechanical properties of the sintered samples reflected their relative density. The maximum values of Young’s modulus (450 ± 10 GPa), bending strength (840 ± 40 MPa) and hardness (35 ± 4 GPa) were obtained for fully dense specimens fabricated from the synthesized B 6.3 C-21vol%TiB 2 mixture.