The switching behaviors of ionic/electronic mixed conductor-based solid electrolyte nonvolatile memories have been attributed to repetitive formation and breakage of the conductive pathways inside a solid electrolyte. However, direct evidence of such pathway existence and their formations has never been provided. Herein, we reproduced the switching behavior of a Ag/Ag(2)S/W sandwich structure inside a high-resolution transmission electron microscope equipped with a scanning tunneling microscope unit. The on/off current ratio of 5 orders of magnitude was documented. The in situ formation and breakage of a nanoscale conductive channel were ultimately verified in real time and under atomic resolution. We found that a conducting Ag(2)S argentite phase and a Ag nanocrystal together formed the ionic and electronic conductive channel. The preferential atomic sites for Ag nanocrystal growth within the argentite phase were finally clarified.