Experimental evidence is presented that electron mirror microscopy is particularly well suited for direct visual observation of magnetic stray fields at grain boundaries in magnetic materials. Silicon‐iron disks were used as specimens. By mounting these specimens on a special magnetic stage of axial symmetry, the appearance and the growth of magnetic stray fields with increasing external applied magnetic fields could be observed directly, and motion picture recordings were taken from the viewing screen of the microscope. A series of electron mirror micrographs shown demonstrates that grain boundaries behave quite differently stray field‐wise. The fact that magnetic stray fields on grain boundaries are now accessible to direct visual observation is considered valuable for many magnetic investigations. The still controversial subject of grain size effects on the magnetic properties of such important magnetic materials as silicon‐iron is one subject which might profit from these potentialities inherent in electron mirror microscopy. This electronic observation method might also be helpful in grain boundary studies concerned with the basic physics of magnetics in such narrow regions of distorted order.