Abstract: In this paper, 3 mm thick AZ31 magnesium alloy plate was friction stir processed (FSPed). In the ambient mixed solution of 5%wt NaCl with the addition of different concentrations of sodium carbonate (Na2CO3), the effect of Na2CO3 on the corrosion behavior of friction stir processed AZ31 magnesium alloy and the base metal was evaluated with potentiodynamic polarization curve test and electrochemical impedance spectroscopy (EIS). The results indicate that after addition of the inhibitor, both corrosion current densities of FSPed magnesium alloy and base metal reduced, the polarization resistance and charge transfer resistance increased. Meanwhile, the inhibition efficiency of FSPed magnesium alloy was higher than that of the base metal, and the inhibition efficiency increased with the concentration of Na2CO3. The sodium carbonate acted as an effective inorganic inhibitor, and the inhibition effect was related with the metal surface condition.