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.m^_1/2, respectively.