Magnesium (Mg) alloys are very attractive materials for structural applications because of excellent specific strength. However, their absolute strengths are insufficient, thus it is necessary to further improve the mechanical properties, particularly fatigue strength. One of the methods for improving mechanical properties is grain refinement, but studies on grain refinement in Mg alloys are very limited (Yamashita
]). The purpose of the present study is to achieve grain refinement due to controlled extrusion and associated improvement of fatigue strength in wrought Mg alloys. First, grain refinement due to extrusion was studied and then the fatigue behaviour of the extruded materials was discussed.