A high-pressure phase transition ofAl2O3from the corundum structure to theRh2O3(II)structure at over 70 GPa has been theoretically predicted, while sufficient experimental evidences have not been reported. In this study, the Hugoniot-measurement experiments were performed on a corundum-structureAl2O3single crystal to obtain the informations about the high-pressure polymorph. The Hugoniot parameters were measured by the inclined-mirror method in the pressure range up to over 100 GPa. A possible kink due to phase transition was observed on the inclined-mirror images in the pressure range higher than 70 GPa. ©2000 American Institute of Physics.