Al2O3/Al composite was fabricated by the reaction between SiO2 and molten aluminum.The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO2.The morphologies of Al2O3 have different features,depending on the reaction temperature.The composite has equiaxed Al2O3 grains when materials reacted below 1200℃,and the composite is composed of a large number of fine Al2O3 grains and aluminum.The composite has a frame-shaped Al2O3 microstructure at the reaction temperature of above 1250℃.