The effect of Sm (0 wt.%-2 wt.%) addition on the corrosion behavior of Mg-6Al-1.2Y-0.9Nd alloy in 3.5 wt.% NaCl solution has been studied by static corrosion tests, corrosion morphology observation, corrosion scale and microstructure analysis. The results show that, with the increasing of Sm content, the corrosion rate of the alloy decreases at first, then increases and reaches the valley at 0.5 wt.% Sm. The reason is that the proper content of Sm addition can refine the precipitates and make the component and microstructure uniform, and therefore, it remarkably improves the corrosion resistance of the alloy.