The deformation mechanism of extruded AZ31 magnesium alloy rod under various temperature conditions was studied. The deformation mechanism was made clear by the changes of microstructures. The clarified mechanism was particularly what acts on the orientation for which trans granular sliding and grain boundary sliding are restrained. From the result, the yield mechanism of AZ31 magnesium alloy is non basal slip to 673K from 423K. The non basal slip works before the fracture under the temperature below 573K. At a temperature of 573K or higher, grain boundary sliding is activated.
