Experiments were conducted to evaluate the evolution of structure and hardness in processing by high-pressure torsion (HPT) of the magnesium AZ91 and AZ31 alloys. Both alloys were processed by HPT at room temperature for 1/4, 1, and 5 turns using a rotation speed of 1 rpm. Structure observations and microhardness measurements were undertaken on vertical cross-sectional planes cut through the HPT disks. The results demonstrate that the deformation is heterogeneous across the vertical cross sections but with a gradual evolution toward homogeneity with increasing numbers of revolutions.