Si₃N₄/10vol% TiN particulate composites with six TiN particle size distributions (average size: 0.3-13.6μm) were sintered at 1850°C for 4h in 0.9MPa N₂ atmosphere, and Young's modulus, fracture toughness and microstructure of the composites were examined. Although all the composites were densified up to >98% theoretical density, Young's modulus of the composites with larger TiN particles decreased due to the pre-existing microcracks. Fracture toughness of the composites showed a maximum value at the particle size of TiN of about 4μm, which is smaller than the predicted critical size. It is suggested that the presence of the grain-boundary phases in the composite favors the formation of microcracks at smaller TiN particles.