Abstract Ion implantation into ceramic materials changes their mechanical properties. These changes are also affected by the substrate, however. To examine the effect of ion implantation without the effect of the substrate, in this study α-Alumina particles (average diameter of 2 μm) were implanted with 2.6 MeV Al ions at an ion dose of 1 × 10 17 cm − 2 . The implantation introduced the defect, such as vacancies and interstitial atoms, into entire particle, because the penetration depth of 2.6 MeV ions was comparable to the diameter of the particles. The compression test of ion-implanted particles was performed to evaluate their strength. The ion implantation had little effect on the strength of the particles, indicating that the defect induced by the implantation does not directly determine the strength of the Al 2O 3 particles. The result was compared with the result of bulk Al 2O 3 (sapphire (11¯02) surface). The implantation into bulk sapphire increased the fracture toughness, K 1 C , of the surface, this increase of the fracture toughness was responsible for the residual stress induced by the ion implantation.