Dislocation structures in fatigued  coplanar double-slip-oriented copper single crystals were studied using the electron channelling contrast technique in scanning electron microscopy, especially focusing on the observations of the microstructures of persistent slip bands and deformation bands. It was found that, at low plastic strain amplitudes (γ pl ≤ 3.4 × 10 – 4 ), the dislocation structures of the  copper single crystal comprise a majority of elongated veins and a few elongated cells along the primary slip plane (111). As γ pl increases to 6.2 × 10 – 4 , a special persistent slip band structure consisting of irregular dislocation cells, rather than generally-observed ladders in single-slip crystals, was found to form, which is responsible for the occurrence of a quasi-plateau in the cyclic stress – strain curve of the  crystal. When γ pl ≤ 3.5 × 10 – 3 , different dislocation microstructures in deformation bands, such as wall-like features, dislocation walls, elongated cells and dense dislocation cells, were found in the cyclically saturated  crystal. Effects of the crystallographic orientation, the applied plastic strain amplitude, the accumulated plastic strain and the strain localization in the crystal on the microstructure of deformation bands are summarized and discussed.