Variations in the number and mobility of domain walls have been proposed as explanations for the frequency dependence of losses in 3% Si‐Fe. In order to test these explanations, the domain structure in (110)[001] grain‐oriented 3% Si‐Fe was photographed during transversal of individual magnetization cycles using high speed Kerr cinematography. Measurements of wall velocity revealed a dependence of wall mobility on magnetizing frequency over the frequency range from 0.1 to 10 Hz with no change in the number of walls. From 10 to 100 Hz, the number of walls increased; however, the rate of increase was less than that predicted, and the newly created walls were not present during the entire magnetization cycle.