An upright seawall with floating panels was proposed in this study in order to mitigate wave overtopping disasters induced by storm surge or high wave. Laboratory experiments were carried out using a two-dimensional wave flume for confirming the effectiveness of the floating panel as a countermeasure against wave overtopping and examining the dynamic behavior of the floating panel. As a result the floating panel was found to have a great reduction effect of wave overtopping under regular wave action as well as infragravity wave action by following the water surface elevation in front of the seawall. It was also confirmed that the phase lag between the behaviors of the floating panel and the water surface increases as wave period approaches the natural period of the vertical oscillation of the floating panel.
