Reactive hot-press (1800-1880 degreesC, 30 MPa, vacuum) is used to fabricate relatively dense B4C matrix light composites with the sintering additive of (Al2O3 + Y2O3). Phase composition, microstructure and mechanical properties are determined by methods of XRD, SEM and SENB, etc. These results show that reactions among original powders B4C, Si3N4 and TiC occur during sintering and new phases as SiC, TiB2 and BN are produced. The sandwich SiC and claviform TiB2 play an important role in improving the properties. The composites are ultimately and compactly sintered owing to higher temperature, fine grains and liquid phase sintering, with the highest relative density of 95.6%. The composite sintered at 1880 degreesC possesses the best general properties with bending strength of 540 MPa. and fracture toughness of 5.6 MPa m(1/2), 29 and 80% higher than that of monolithic B4C, respectively. The fracture mode is the combination of transgranular fracture and intergranular fracture. The toughening mechanism is certified to consist of crack deflection, crack bridging and pulling-out effects of the grains. (C) 2004 Published by Elsevier Ltd.