The corrosion behavior of AM50 and AZ91D Mg alloys containing 0.2 wt% to 1.0 wt% Gd was evaluated in 3.5 wt% sodium chloride (NaCl) solution using electrochemical, gravimetric, and hydrogen evolution methods. Corrosion products were examined using scanning electron microscopy and low-angle x-ray diffraction. Gd addition reduced the volume fraction of β-Mg 17Al 12 phase because of the precipitation of Al 2Gd and Al-Mn-Gd intermetallic compounds, which revealed lower surface potential than Al-Mn inclusions in the unmodified alloys. The corrosion rate of AM50 and AZ91D alloys decreased with the addition of Gd by 85% to 93%. This effect was associated mainly with the decreased rate of cathodic reaction kinetics because of the suppression of microgalvanic corrosion between primary and secondary phases. © 2012, NACE International.