Abstract: TiB₂/Al-Si composites were prepared by stir casting method. The effects of different contents of micro/nano TiB₂ particles on the mechanical properties of composites were investigated. The results show that TiB₂ particles effectively refine the microstructure of Al-Si matrix alloy and improve the mechanical properties of Al-Si matrix alloy. When the content of nano-TiB₂ particles reaches 1.5 wt%, the tensile strength and elongation of TiB₂/Al-Si composites reach 344.69 MPa and 6.64%, respectively, which are 17.9% and 55.5% higher than those of the matrix alloy. When the content of TiB₂ particles reaches 0.8 wt%, the tensile strength and elongation of TiB₂/Al-Si composites reach 334.90 MPa and 7.50%, respectively,which are 14.4% and 75.6% higher than those of the matrix alloy. The mechanical properties of micro/nanocomposites are improved by the strengthening mechanisms of fine grain strengthening, second phase strengthening, CTE strengthening, and Orowan strengthening also plays an important role in nanocomposites; the fracture mechanism of nanoparticle-reinforced composites is a brittle-ductile mixed fracture mechanism with brittle fracture as the main mechanism; and the fracture of micrometer-particle-reinforced composites is a brittle-ductile mixed fracture mechanism with ductile fracture as the main mechanism.