Abstract: The welding by one side and by both sides of Mg/Al clad sheets was conducted, and the microstructure and mechanical properties of Mg/Al clad sheets butt joints was tested using friction stir welding method.The results showed that with the increase of welding and rotating speed, the good weld surface appearance was obtained and no porosities and cracks were observed. The joint phase was mainly consisted of Mg₁₇Al₁₂, Mg₂Al₃ and MgAl phases, the size of grain is effectively refined and the dynamic recrystallization takes place. The formation of brittle intermetallic compounds is benefits to the formation of the recrystallization nucleus. Compared with joints with friction stir welding by one side, the joints of welding by both sides has much higher tensile strength and elongation due to the different distribution and quality of intermetallic compounds in welding joint. Inhibiting the formation of intermetallic compounds at the joints is beneficial to improve the performance of Mg/Al clad sheets of FSW joints.