Polycrystalline magnesium are generally fractured intergranularly under dynamic loading, and exhibits limited ductility owing to its HCP structure. In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for two commercial magnesium alloys, ZK60 and AZ31. It was found that the strength and ductility of magnesium alloys were enhanced by refining the grain structure. Further enhancement of ductility can be achieved by a simple shear through equal-channel-angular-extrusion (ECAE) process. A commercial AZ31 alloy was subjected to ECAE followed by annealing to develop a different texture compared with the directly-extruded alloy. During the dynamic tensile test, elongation-to-failure was more than twice higher than that of the directly-extruded alloy. It has been demonstrated that, for commercial magnesium alloys, the improvement of strength-ductility balance can be achieved by controlling the grain structure.