A case study of seismic response of an earth embankment foundation on liquefiable soils in Kansai area, west Japan was presented. Based on a calibrated cyclic elasto-plastic constitutive model for liquefiable sand and Biot dynamic coupled theory, the seismic analysis was carried out by using a dynamic effective stress finite element method under plane strain condition. A recent design study was illustrated in detail for a river earth embankment subjected to seismic excitation on the saturated deposits with liquefiable sands. Simulated results of the embankment foundation during liquefaction were obtained for acceleration, displacement, and excess pore water pressures, which were considered to yield useful results for earthquake geotechnical design. The results show that the foundation soil reaches a fully liquefied state with high excess pore pressure ratios approaching to 1.0 due to the earthquake shaking. At the end of the earthquake, the extensive liquefaction causes about 1.0 m lateral spreading at the toe and 60 cm settlement at the crest of the earth embankment.