Pure MoSi2 and MoSi2 composites with different volume fraction of SiC particles were prepared by the technology of in situ reaction and hot pressing the pure powder of Mo, Si and C after alcohol mixing. The effects of in situ formed SiC particles on the microstructure, the flexural strength and fracture toughness of SiCP/MoSi2 composites were studied. The research shows the relative density, flexural strength and fracture toughness of the composites are increased compared with those of the pure MoSi2 material. It is found that the in–situ formed SiC particles refine the MoSi2 grains and eliminate the brittle SiO2 glass phase. The strengthening mechanism of the composites is of the refinement of MoSi2 grains,dispersion strengthening of the in–situ formed SiC particles and elimination of the brittle SiO2 glass phase.