This study presents an application of high-pressure torsion (HPT) to an Al-Li-Cu-Mg alloy (2091). The alloy was subjected to solid solution treatment at 505°C for 30 minutes and was processed by HPT under 6 GPa for 5 revolutions at room temperature. The hardness increased with straining and saturated to a constant level at 225 Hv. Aging was undertaken on the HPT-processed alloy at 100, 150 and 190°C for the total periods up to 9.3 days. The aging treatment led to a further increase in the hardness to ∼275 Hv. It is shown that the simultaneous strengthening of the alloy due to grain refinement and age hardening was successfully achieved by application of HPT and subsequent aging treatment. The enhancement of the strength is prominent when compared with the application of a conventional rolling process.