Rainfall reduces the seismic resistance of an embankment if the drainage system of the embankment is inadequate; however, it is not considered in practical seismic design. In this study, a method to consider the effect of rain-fall on the seismic performance of embankments was introduced with the shaking table test results and a case history. A FEM code 'FLIP' with a model of ground strength reduction due to rainfall is described.