Abstract: Aluminum foam projectiles were used to dynamically load clamped quadrate sandwich plates with an aluminum foam core and monolithic solid plates. A laser Doppler velocimeter and a laser displacement transducer were applied to measure the impact velocities of the foam projectiles and the deflection-time histories at the midpoints of the back faces of the plates,respectively. Deformation and failure modes of the sandwich and monolithic plates were exhibited to discuss the effects of the projectile impulse,the face sheet thickness and the core density and thickness on the structural responses of the plates. It is found that there is the maximum permanent deflection at the midpoint of the back face,the deflection at the plate brim is the least and the whole deformation profile takes on a dome shape with flower-shaped deformation. The results indicate that the permanent deflection of the back face can be effectively controlled to improve the capacity of energy absorption of sandwich plates by increasing the face sheet or core thickness. The structural response is sensitive to the projectile impulse or the core density and the permanent deflection is proportional to the projectile impulse or the core density. The experimental results can provide help for the optimum design of cellular metallic sandwich structures.