Thermal stimulated current in Al2O3 single crystal and sandwiched Al2O3 single crystal-Bi2O3-Al2O3 single crystal samples was measured during the heating， soaking and cooling processes. It was found that the thermal stimulated current can be detected in sandwiched samples， while no current was observed in the Al2O3 single crystal sample. With the increase of heating rate， the thermal stimulated current measured during cooling decreases， which implies that the thermal stimulated current is induced by defect ions. The calculation of active energy shows that there are two kinds of defect ions involved in producing the thermal stimulated current.