Abstract: The welded samples of 6061/AZ31B heterogeneous alloy plates were prepared by friction stir welding. With the help of OM, SEM, EDS and XRD, the microstructure of the welded joint from the weld to the base metal were studied.The corrosion characteristics of the weld and base metals were studied by the NaCl solution immersion corrosion method and electrochemical corrosion tests. The results show that the structure of the weld at aluminum side is relatively uniform, while non-uniform band-like structure composed of magnesium-rich and aluminum-rich bands is formed in the weld at the magnesium side. In the corrosion test, the weld at the aluminum side is passivated, and its corrosion resistance is better than that of the aluminum base material, and only slight pitting and intergranular corrosion behaviors are shown. Compared with the magnesium base metal, the grain refinement of the weld at the magnesium side improves its corrosion resistance. The corrosion morphology of the magnesium-rich zone of the weld at the magnesium side is similar to that of the magnesium base material, obvious corrosion products and corrosion cracks are formed on the surface of the alloy. However, only slight pitting corrosion occurs in the aluminum-rich zone.