In this study, the Al-Li 2198-T8 (T8: under artificially peak-aged condition) alloy was fabricated by high pressure torsion (HPT) and then subjected to heat treatment at 175. °C for different durations. The microstructural evolution, mechanical property and thermal stability of the HPT-processed alloy were studied. The results demonstrate that the precipitates appeared in the as-received alloy were dissolved into the matrix after HPT processing; and the grains were significantly refined, accompanied by the modification of dislocations. The dislocation density gradually increased along the radial direction from the centre to the edge of the obtained disk. The improvement of tensile strength of HPT-processed 2198-T8 alloy was dominantly associated with grain refinement and dislocation strengthening. The subsequent heat treatment of the HPT-processed alloy led to slight grain growth and reduction of dislocation density. Also, no strengthening phases precipitated out during the post heat treatment. These factors accounted for the decrease of tensile property for HPT 2198-T8 alloy aged at 175. °C for up to 12. h, suggesting a low thermal stability.