An AZ31 magnesium alloy was processed by high-pressure torsion (HPT) at room temperature under an imposed pressure of 6.0 GPa. Microstructural analysis showed that the HPT processing introduced significant grain refinement with a reduction in grain size from similar to 35 mu m in the initial annealed condition to similar to 110 nm after ten turns of HPT. Microhardness measurements showed that a reasonable level of hardness homogeneity was achieved across the disk processed through ten turns. The results from tensile testing demonstrated that the ultrafine-grained (UFG) AZ31 alloy processed by HPT exhibits high ductility with a maximum elongation of similar to 400 % at the relatively low testing temperature of 423 K. The results confirm that the UFG AZ31 magnesium alloy processed by HPT through ten turns has a strong potential for use in micro-forming applications.