Abstract: (Al2O3＋Al3Zr)p/A356 composites were synthesized by micro-alloying and melt in-situ reaction technology.The effect of micro-alloying on microstructure and mechanical properties of the composites was investigated.The results indicate that the reinforced particulates Al2O3 and Al3Zr of the composites after alloying became smaller with the size at about 0.5-2 μm,the distribution became more homogeneous,the morphology became spherical and the surrounding was blunt.The mechanical properties of the composites were greatly enhanced,compared with that of the composites without alloying element addition.The tensile strength,yield strength and elongation of the (Al2O3+Al3Zr)p/A356 composites reached 379 MPa,297 MPa and 7.6%,which increased 325%,37.5% and 59.5% respectively,after 0.2wt%Mn,0.2wt%Cr and 0.3wt%RE were added.The fracture of the composites was ductile fracture.The strengthening mechanisms included Orowan strengthening,grain-refined strengthening,solid-solution strengthening and dislocation strengthening.