The structure evolution of polycrystalline magnesium after high-pressure torsion at room temperature has been investigated. In the initial stages of deformation (yielding) was observed band structures. It has been found out that after 5° shearing the main deformation mode is twinning on the plane Under conditions of 90° shearing cells, grains with a high level of internal stress, a small fraction of recrystallized grains and fragments were identified by the electron-microscopy method. At high degrees of deformation (1—5 rpm) were observed uniformly distributed recrystallized grains, deformed grains and fragments, the clearly expressed basal texture.