The microstructures of friction stir welded (FSW) joint of 2024 aluminum alloy were examined by using optical microscope and transmission electron microscope. The corrosion behaviors of the joint were investigated by method of acid salt spray. The analysis results of microstructure show that the arc stripe is the main feature on the surface of the weld seam due to the extrusion action of the shoulder of the stir tool. The grain and second phase particles are also refined. The second phase particles are mainly composed of Al2CuMg(S phase) and CuAl2(θ phase). The corrosion test shows that the resistance to corrosion of FSW seam is lower than that of base metal pure aluminum layer. There exists an unevenness for the corrosion of the FSW seam. The corrosion initially results from pitting corrosion and finally develops to exfoliation.