Atmospheric corrosion behaviour of cast and as-extruded AM60 Mg alloy was studied in this paper. The results showed that the corrosion rate of cast alloy was higher than that of as-extruded alloy. α-Mg-Mg17Al12 eutectics in cast alloy had better corrosion resistance than α-Mg phase in outdoor atmospheric environment, which would lead to the α-Mg phase being corroded seriously than the nearby eutectics. Then, the corrosion films on as-extruded alloy would not be uniform and had a poor protective effect. The maxium depth of corrosion pit in as-extruded alloy was deeper than that in cast alloy. The as-extruded alloy had much uniform mircrostructures and did not contain eutectics than cast alloy, which caused the corrosion film formed on surface of the former had better protection effect than that on the latter’s surface. Extruded process can not lead to a decrease in atmospheric corrosion resistance of AM60 Mg alloy.