The chemical composition of an Al alloy will influence the properties of Al alloy matrix composites. In this paper, Al₂O₃ particles / Al alloy metal matrix composites were made by high pressure infiltration, and the influence of Al alloy chemical composition, especially Si content, on the mechanical properties (strength and toughness) of the Al alloy matrix composites was studied. The Si content of the Al alloy was changed, and other elements were added to examine their influence on the mechanical properties. The results obtained were as follows: when Cu and Ni were added to the Al alloy, the bending strength of the composites was improved at high temperature. Increasing the alumina volume fraction also improved the bending strength. However increasing the Si content decreased the fracture toughness. The possibility of improving heat-resistance of Al₂O₃ particles reinforced Al composite was found.