Weight reduction of automobiles is one of the effective methods to reduce greenhouse gas emissions. The use of magnesium may allow weight reduction of automobiles due to the low density. However, it is difficult to apply magnesium for structural components, and plastic working methods under dynamic loading, such as high-speed rolling, are not established because the material exhibits limited ductility. To establish their method, the basic understanding about deformation mechanism under dynamic loading at elevated temperature is essential. In this study, we conducted compression test under dynamic loading at elevated temperature in order to clarify the deformation mechanism of magnesium. The results showed that high ductility was obtained over 573K while low ductility was below 473K. Deformed microstructure obtained with SEM/EBSD to clarify the effect of temperature.