Abstract: The effects of SiC particle diamater on the microstructure and tensile properties of spray-formed SiC particle reinforced Al-Si alloy composites were investigated. The results show that the addition of the SiC particles increased the elastic modulus, but decreased the tensile strength and elongation of the composites compared with those of the Al-Si alloy matrix. The SiC particles in both composites were partially aligned along the extrusion direction. When the diameter of SiC particle increased, the degree of orientations increased. The small SiC particles with diameter of 4.5 μm had smaller interparticle spacing and shared more portion of loading than that of SiC particles with the diameter of 20 μm. Therefore, the composites with small reinforcements were better than the composites with big reinforcements in elastic modulus and tensile strength. The interfacial debonding between the SiC particles and the matrix was the main fracture mechanism of the composites with small particles, while the cracking of the SiC particles was dominant in the composite with coarse particles.