Metallic foams are expected to be used as the impact energy absorber material because of their unique deformation characteristics, which almost constant compressive stress appears in a wide range of strain. This phenomenon is well known as the regime of collapse plateau. It is very important to know strain rate dependence of the plateau stress, and the impact energy for suitable design of automotive components. Only limited amount of mechanical response data of metallic foams under dynamic loading are, however, available comparing with those of polymeric foams. In this study, the absorbed energy of an open-celled magnesium foams with a relative density of 0.03-0.06 is evaluated at a dynamic strain rate of similar to 10(3) s(-1) in compression by using the split Hopkinson pressure bar apparatus. In order to investigate the effect of microstructure in the solid material, solution treatment and aging are performed to all the specimens and then examined for the same strain rates. Peak stress and plateau stress per (relative density)(3/2) for as-received and heat treated AZ91 foams showed the strain rate dependence, which decreased by the heat treatment. Therefore, it is possible to control the absorption energy of the AZ91 metallic foam by means of microstructural improvement, which controls the ductility in the solid material. (C) 2001 Published by Elsevier Science B.V.