Abstract: Sub-micron Si3N4 particles reinforced MoSi2 matrix composites prepared by hot pressing had been studied.Through observation of the microstructure of MoSi2-based composite and the measurement of bending strength,micro-hardness and fracture toughness,the strengthening-toughening mechanism of this material was revealed.It is shown that the strengthening mechanism of the composites is the effect of dispersion strengthening and grain refining,and the toughening mechanism is a synthetic effect in terms of grain refining,micro-crack forming,crack deflection and crack branching.The room fracture toughness of Si3N4/MoSi2 composite is 8.2 MPa·m1/2.