Paper presented at GeoFrontiers 2011. The seismic behavior of pile foundations in soft clays is a very complex problem with interacting piles, soils and superstructure. Using ground improvement, for example, Cement Deep Soil Mixing (CDSM), to restrict lateral displacements of piles during earthquakes is a viable, but not fully explored technique. This paper presents experimental methods and procedures for centrifuge tests on single piles with and without ground improvement under both static and dynamic loadings. The data collected from the centrifuge test were used to analyze the differences between piles in unimproved and CDSM-improved soft clay. The test results confirmed that the CDSM can improve the seismic behavior of pile foundations and demonstrated that the pile response is directly related to the size of the ground improvement zone.