Major earthquakes such as Kobe (1995), Kocaeli (1999) and Chi-Chi (Taiwan) have shown that underground structures have suffered significant damage due to dynamic loading. Therefore, recently, much priority has been given to seismic safety of underground structures located in earthquake-prone regions. There is, however, not much experimental research on the dynamic response of buried structures. This research aims to better understand the dynamic behavior of relatively flexible rectangular underground structures embedded in dry sand. To achieve this purpose, a series of dynamic centrifuge tests were conducted on a box-shaped flexible underground structure under harmonic motions with different accelerations and frequencies. Thus, response of soil and buried structure model was examined considering the dynamic soil structure interaction. Accelerometers were placed in the soil and on the buried structure model to evaluate the shear strain and acceleration response. Moreover, a special attempt was made to investigate the racking deformations by installing extensometers inside the tunnel model. Measurements obtained from those extensometers were compared with the predictions of analytical solutions. Results show that, Penzien's approach gives reasonable estimates of racking deformation for the rectangular shaped flexible underground structure.