The effects of strain amplitude and strain ratios in low cycle fatigue (LCF) at 0.25 Hz on the final stable dislocation structure of a failure specimen are investigated in a SAF 2205 duplex stainless steel. The morphology of the fatigued dislocation microstructure in alpha phase consists of dislocation cell structures and persistent slip bands (PSBs). No dislocation loop patches or labyrinths were observed in the a grains. Instead, persistent slip bands (PSBs) and wormlike PSB loops embedded in a highly dense dislocation matrix were found, and the dislocation density increases with the increase of the strain amplitude and tensile mean strain, which chances the strain ratio. The morphology of fatigued dislocation structure in the gamma phase is characterized by the strain-induced martensite. (c) 2005 Elsevier B.V. All rights reserved.