The age-hardenable Mg-4.7%Y-4.6%Gd-0.3%Zr (wt%) alloy has been studied after high pressure torsion (HPT) at room temperature, 200 °C and 300 °C. The formation of partially nanocrystalline structure upon HPT results in substantial strengthening relative to the undeformed state of the alloy. The research showed that the strength of the HPT processed alloy could be further improved by aging.