It is very important to determine the structure of electrode/electrolyte interface in situ not only for the study of fundamental surface science but also for the applications related to nanotechnology. Surface X-ray scattering (SXS) technique is one of the most promising methods to determine the interfacial structure with a high spatial resolution in situ. Here we focus on the SXS technique that enables to probe an interfacial structure even at solid/liquid interface. As an example, we described our results about the structural analyses of the electrochemical deposition processes of Pd and Ag on Au single crystal electrodes using the in situ SXS technique.