B4C-TiB2-CNT ceramic composites were fabricated by the liquid silicon infiltration (LSI) sintering at 1 500 ℃ in vacuum. The compositions, morphologies, mechanical properties and toughening mechanism of the fabricated composites were investigated. The results show that the main constituent phases of the composites are B12(C, Si, B)3, SiC and Si. The additions of TiB2 and CNT significantly improve the mechanical properties of liquid-phase silicon sintered B4C ceramics. The flexural strength and fracture toughness of the composite ceramics reach (390±18) MPa and (5.38±0.38) MPa·m1/2 with TiB2 and CNT additions of 10% and 0.4% respectively, which are 31% and 53% higher than pure B4C caremics. The toughening mechanisms of B4C-TiB2-CNT ceramic composites are explained by the pullout of plate-like SiC particles and CNT, the particle toughening of TiB2 and the deflection of cracks.