AbstractThe major aim of this paper is to describe and characterize qualitatively the saturation dislocation structures in fatigued nickel single crystals with different orientations and to relate them to the mechanical properties. Within the investigated plastic strain amplitude region all measured cyclic stress strain curves exhibit two ranges with a sharp transition. In the first range of the cyclic stress strain curve the dislocation arrangement of the nickel single crystals oriented for single slip is significantly dependent on the plastic strain amplitude, that is the volume of the dislocation‐poor regions decreases at increasing amplitude. In the second range ladder‐like structures of the persistent slip bands and vein‐like structures of the matrix are observed in agreement with the results of copper single crystals. Beside, at great amplitude, but within the second range, there is a steady increase of parquet‐like matrix structures. On [001] single crystals the spatial dislocation structure is characterized by condensed and uncondensed {100} dislocation walls. The limited regions with condensed walls are supposed to be regions of high plastic strain amplitude (“mesoscopic” strain localizations). Amplitude changing tests are suitable to obtain results on the stability of the dislocation structures to increasing amplitude and decreasing amplitude, respectively.