High strain rate superplastic (HSRS) bulging and cavitation behavior of a cold rolled Al-6Mg-0.3Sc sheet were investigated at the temperature of 798K and at the constant applied flow stress of 6.0MPa. The maximum effective strain of about 2.1 was obtained. The experimental results revealed that the cavity growth was essentially plastic - controlled. HSRS bulging limits of the sheet were further predicted based on the Marchiniak-Kuczynski model and a plastic damage approach. It is able to predict HSRS forming limits of the sheet in a reasonable agreement with the experimental findings even without assuming any initial geometrical defect.