A line‐sampling multiframe stroboscopic observation system was attached to a commercial‐type 200‐kV scanning electron microscope for dynamic observation of ferromagnetic domains in grain‐oriented 3% silicon steels with orientation near (110) [001]. This technique has enabled the individual stroboscopic image, at different phases of drive field, to be observed on a display tube simultaneously, leading to a more comprehensive understanding of core‐loss characteristics of the silicon steels magnetized at commercial frequency in practical use. The observation has clearly revealed that uniform displacement of domain walls according to the alternating magnetization at commercial frequency leads to lower core losses during operation.