Magnesium has been proposed as an implant metal due to its low weight and inherent biocompatibility. However, it use as a biomaterial is seriously limited by its poor corrosion n resistance. Die-cast AZ91D and rolled AZ31B alloys, which are commercial magnesium alloys, were used in this study. After plasma anodization, SEM showed that the surface had a relatively high porosity with some micro-cracks. EDX revealed Mg, Al and Zn on the surface of the samples before anodization. After anodization , there was an increase in the oxygen EDX peak intensity with a concomitant decrease in the magnesium intensity . Anodized AZ91D had the best corrosion resistance according to the potentiodynamic polarization curves. After immersion in Hanks solution for 10 days, the untreated AZ31B sample had the highest pH value due to formation of OH- on the film surface.