The Al2O3-TiC/Al composites were prepared by injecting CO2 gas into Ti contained Al-Si alloy melts. The microstructure of the composites was examined by XRD, SEM and TEM. It was indicated that both Al2O3 and TiC particles can be formed by the in situ reaction of CO2 with Ti and Al in the melten alloys. The Al2O3 and TiC particles in size of 0.3~1.5μm distributed uniformly in the matrix. The volume fraction of the particles is mainly depend upon the time of CO2 injection.The tensile strength at room temperature of the composites can reach 346.08MPa and the hardness is 149.6MPa HBS, repectively, which are higher than those of the matrix alloy.