continuous and interrupted torsion tests have been conducted in the temperature range of 320-520℃ at constant strain rates of 1.26-5.71×10^-3 sec^-1 on an Al-Cu-Mg alloy. During the continuous deformation, dynamic recrystallization was observed above 370℃ and the nuclcation of the recrystallization at dislocation clusters or adjacent to second phase particle. The presence of deformation substructure in the recrystallized grain provided a direct evidence that recrystallization had occurred during the deformation. In the interrupted tests, duration of the interruptions were 10, 20, or 40 sec at egual strain intervals of either 0.4 or 0.6. During the interrupted deformation, the major softening mechanism was static recovery and partially static recrystallization above 370℃. The degree of softening was augmented by increase in the temperature, the interruption strain, and the interruption time.