Titanium-oxide (TiO2 ) memristors exposed to 1-MeV alpha particles exhibit only minor changes in the electrical response for ion fluencies up to 1014 cm - 2. At higher fluence levels, virgin and off-state devices exhibit measurable increases in current conduction between the two platinum (Pt) electrodes. Analysis, supported by radiation transport and numerical device simulations, suggests that radiation-induced displacement damage in the TiO2 film increases the density of oxygen vacancies, thereby altering both resistivity in the bulk of the transition-metal oxide and the junction characteristics of Pt-TiO2 interface. Nevertheless, the experimental results indicate continued switching functionality of the memristors even after exposure to 1015 cm- 2 alpha particles. The high intrinsic vacancy density in the devices prior to radiation exposure is identified as the primary feature contributing to apparent radiation hardness.