Abstract:The B4C/C preforms were prepared by the gel-casting and the B4C-SiC-Si composites were fabricated based on liquid silicon infiltration process. The effects of different catalysts (Na2CO3, NaOH, KOH, Na2SiO3 and NaHCO3)on the microstructure and mechanical properties of B4C-SiC-Si composites were investigated. The results showed that the catalyst mainly affected the microstructural uniformity of composites and the size of residual Si. The composites were mainly composed of B4C, B12(B,C,Si)3, SiC and Si. When NaOH, KOH or NaHCO3as catalyst, the distribution of residual Si was uniform. With the NaOH as catalyst, the mechanical properties of B4C-SiC-Si composites were the best:the hardness, flexural strength and fracture toughness were 16.9 GPa, 296 MPa and 4.15 MPa.m1/2, respectively.