Abstract: The double-sided friction stir welding process were used to weld 6061 aluminum alloy with the thickness of 30 mm, and the microstructure, micro-hardness and corrosion resistance of the welded joints were analyzed and tested by means of metallographic microscope, micro-hardness tester and electrochemical workstation. The metallographic observation shows that there is an obvious boundary between the advancing side of the friction stir welded joint and the base metal, while the boundary of retreating side and the base metal is blurred, the grains in weld nugget zone are homogeneous and fine equiaxed crystal. The micro-hardness curve of friction stir welded joints shows a “W” shape. The minimum micro-hardness appears in the heat affected zone. The corrosion test shows that the corrosion current is larger in the overlapping area of double-side welded joints, once the corrosion is started, the corrosion speed is very fast, and the corrosion resistance is relatively poor.