Al/nano-SiC composite was fabricated to investigate the effect of the additional nano-particulate on corrosion resistance and its mechanism by friction stir processing. Corrosion resistance of specimens was detected through electrochemical impedance spectroscopy and potentiodynamic polarization techniques in 3.5% NaCl solution at room temperature. Electron back-scattered diffraction and transmission electron microscopy were employed for thorough microstructural characterization to investigate the corrosion resistance variation mechanism of three specimens. After FSP, the specimens impedance increased significantly, and the corrosion potential for base metal, FSP sample and composite were –1.517, –1.338 and –1.339 V and the corrosion current density for them are 0.48, 0.11 and 0.12 mA/cm2, respectively. The grain structure of specimens fabricated by friction stir processing was composed of isometric crystal grain with an average grain size of about 8.7 μm, and most of the precipitates dissolved due to high temperature. However, the addition of nano SiC particles further reduced the grain size to about 4.1 μm. The corrosion resistance of Al6061/nano-SiC composite is higher than base metal, but weaker than FSP sample. The difference between SiC and matrix forms the corrosive cell, which has a negative effect on corrosion resistance. The increase of the number of grain boundaries leads to the increase of lattice vacancy and other defects, which results in the increase of charge transfer resistance to improve the corrosion resistance.