The magnetic domain structure was studied in a 0.17 cm wide ×32 μm thick ribbon of a Ni 40Fe40P14B6 amorphous alloy (Metglas Alloy 2826 manufactured by Allied Chemical during dc and ac magnetization after stress relief annealing and under various levels of applied tensile stress. The longitudinal Kerr effect was used for domain observation. Under an applied tensile stress, a simple antiparallel 180° wall structure was observed and the flux density of the sample correlated well with the observed 180° wall displacement. The domain wall spacing/sheet thickness ratio (2L/d) was extremely large (∠48) and decreased with increasing magnetizing frequency and applied tensile stress; the dependence of 2L/d on magnetizing frequency is characteristic of systems in which domain wall motion is eddy current limited. Significant improvements in losses and permeability during magnetization at power frequencies will occur if methods can be found to reduce these rather large domain wall spacings.