The aluminum metal matrix composites (Al MMCs) reinforced by SiC particles with different sizes (25 nm, 150 nm and 3.5 m) were fabricated by powder metallurgy technique, and the microstructure and tensile properties of the Al MMCs were investigated. When the volume fraction of SiC particles is fixed to be 5 %, the Al MMCs reinforced by nanosized and submicron particles exhibit much higher ultimate tensile strength and yield strength, and much lower ductility compared with those of the non-reinforced aluminum. However, for the MMC reinforced by 3.5 m SiC particles, almost no strengthening effect is found. The strengthening effect of the Al MMCs is analyzed in terms of dislocation mechanism. Moreover, the tensile fracture surface shows that the damage mechanism of the Al MMCs can be changed as the size of SiC particles is changed.