Abstract: Friction stir butt welding of 3 mm thick AZ31 extruded magnesium alloy sheet was conducted. The electrochemical behaviors of AZ31 magnesium alloy friction stir weld and the parent metal were studied with static weight loss method, potentiodynamic polarization curve and electrochemical impedance spectroscopy(EIS) test in 5% NaCl aqueous solution at room temperature. The results indicate the average corrosion rates of AZ31 parent metal and weld after 168 hours' immersion were 0.154 and 0.135 g/(m²·h), respectively; the corrosion current densities of AZ31 parent metal and weld were 0.001 63 and 0.000 45 A/cm², respectively; the polarization resistance were 9.553 and 12.61 Ω/cm², respectively. The results show that the anti-corrosion property of AZ31 friction stir weld was better than that of the parent metal.