The behaviour of the magnesium alloy AZ61 during one-dimensional shock loading has been investigated in terms of the Hugoniot (shock-induced equation of state) and the shear strength variation in terms of variation with impact stress and pulse duration. The Hugoniot has been shown to be near identical with the similar AZ31, as would be expected with related dilute alloy systems. The shear strength has been observed to increase with applied shock stress, in common with many other materials. The shear strength has also been observed to increase with time behind the shock front. It has been suggested that this be due to twinning early in the deformation process, followed by dislocation based at later stages. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.