An ultralight magnesium alloy AM50A has been investigated for its potential to be used in aerospace and automotive industry. The dynamic stress strain relation of aluminum 6061 T6 and the magnesium alloy AM50A have been obtained by using the Hopkinson bar apparatus. The strain rates range between 600 s-1 and 1300 s-1. The Al 6061 T6 results tally well with those in literature. The magnesium alloy AM50A displays about 50% higher tensile stress at the strain rate of about 1300 s-1 than at static.