The hot deformation behavior of copper has been studied in the temperature range from 0.55 Tm to 0.65 Tm and the strain rate range from 1.26×10(-3) S(-1) to 5.71×10(-3) by hot torsion. The hot softening mechanism of copper has been found to result from dynamic recrystallization through the flow curve and change of microstructure. Strain for the onset of dynamic recrystallization is represented by ε_c=0.039 LnZ-0.531 using Zener-Hollomon parameter Z and strain for the completion of dynamic recrystallization is represented by ε_x=0.276 LnZ-4.571. The time required for dynamically recrystallized grains decreased with increasing deformation temperature and strain rates. The dynamically recrystallized grains are smaller than statically recrystallized grains, and hardness is larger than statically recrystallized grains.