This paper presents a case study on a numerical prediction of seepage and seismic behaviors of an unsaturated fill slope. In this study, the numerical prediction is performed by using a dynamic threephase (soil, water and air) coupled analysis based on porous media theory and constitutive models. In-situ observation at the target fill slope of the case study has been performed since 2006. The ground water level, the soil moisture and the water quantity gushed up from the toe of the fill slope are monitored continuously. These observation data were used for verification of the analysis. First, distributions of water saturation in the fill slope are simulated by performing seepage analyses to reproduce the in-situ ground water level in the fill slope. Next, seismic responses of the fill slope during a future scenario earthquake are predicted under different moisture conditions of unsaturated fill.