The effects of solution-treatment temperature, spinodal decomposition and plastic deformation on the magnetic domains of duplex stainless steel have been investigated. The domain structure is maze-like with spikes and these are not artefacts (unlike Fe–Ga alloys). In the solution-treatment temperature range, the domain structure does not have a big temperaturedependence. Both spinodal decomposition and plastic deformation lead to inhomogeneity and a reduction in size in magnetic domains. However, inhomogeneity in domain structure, among grains orwithin the samegrain, may also exist in the solution-treated condition, albeit to a lesser extent. The maze-like domain structure is unaffected by the change in dislocation structure.