Chromium-implantation of single crystal aluminum oxide (Al²O³) has been shown to be anisotropic with respect to damage accumulation. Ultra-low load indentation and Rutherford backscattering spectroscopy (RBS) have been used to demonstrate the dependence of radiation damage on fluence and crystal orientation. Single crystal Al²O³) specimens of c-axis ([0001] normal to the surface) and a-axis ([1120] normal to the surface) orientations were ion-implanted simultaneously at room temperature with chromium ions of 160-keV energy to flu-ences up to 6 × 10¹⁷ ions cm~2. The implanted specimens were found to possess different near-surface mechanical properties. Subsequent RBS-ion channeling examination indicated different amounts of disorder in both the aluminum and oxygen sublattices for the two orientations. These results imply a higher amorphization threshold in terms of implantation fluence for the a-axis oriented samples.