Atomic force microscopy (AFM) is a powerful technique to characterize solid/liquid interfacial structures on an atomic scale. However, conventional AFM using Si cantilevers can only be applied to optically transparent liquids. In this study, we applied a quartz tuning fork sensor to overcome this issue and succeeded in AFM imaging of the interfacial structures between molten Ga and solid Au−Ga alloys. The crystal structure of the alloy was identified as AuGa 2 from the atomic-resolution imaging results, and the AuGa 2 (111) surfaces were also found to be exposed. In situ observation of the alloy crystal growth was carried out, and its growth mode was discussed. We also found that the interfacial solvation structure of molten Ga can be visualized, which corresponded well to the atomic arrangement of the solid AuGa 2 . Since the molten-and solid-metal interfaces play crucial roles in many metallurgy applications, such as plating, soldering, and brazing, it is of great importance for both scientific and practical purposes to characterize these interfaces at the atomic scale. This study demonstrates the potential of AFM as a new analytical technique of molten-and solid-metal interfaces.