Although comprehensive research findings of the cyclic deformation and dislocation structures of Cu single crystals with various orientations have been well established over the four decades, studies on the thermal stability of dislocation structures in fatigued Cu single crystals are still rarely reported. In the present work, [233] Cu single crystals oriented for coplanar double slip were firstly cyclically deformed at different plastic strain amplitudes γ_pl up to saturation, and then annealed at different temperatures for 30 min.The dislocation structures induced by cyclic deformation as well as the microstructural changes resulting from subsequent annealing treatments were detected by using the electron channeling contrast (ECC) technique in SEM and TEM. It was found that the dislocation structures have undergone an obvious process of recovery at 300 ℃,and the recrystallization even partially takes place in the sample fatigued at highγ_pl. However,at 500 and 800 ℃, the violent recrystallization takes place in all crystals and a large number of annealing twins have appeared. As the plastic strain amplitude and accumulated plastic strain increase, the degree of strain concentration would be significantly aggravated, providing a higher local strain energy for the occurrence of recrystallization and the initiation of twins, so that the recrystallization takes place more noticeably, and annealing twins become coarser and the number of them increases notably. The formation of annealing twins is closely related to the appearance of stacking faults. The DSC measurements demonstrated that the recrystallization process and the formation process of twins should be a gradually-developing process, instead of a suddenly-forming process.