New magnesium alloys (Die-Cast and wrought) have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, high temperature behaviour and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new magnesium alloys: Mg-Al-Ca, Mg-Al-Sr, Mg-Zn-Mn-Si (ZSM) and Mg-Zn-Mn-Si-Ca (ZSMX). These ZSM6X1 and ZSM651+YCa alloys were prepared using hot extrusion. These Mg-Al-Ca and Mg-Al-Sr were prepared using high pressure die cast. AC and DC polarization tests were carried out on the new alloys. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The addition of Si increased the corrosion resistance. The additions of Sr and Ca also affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg alloys such as grain size and precipitates caused by the change in precipitation and recrystallisation behaviour.