We have studied the magnetic properties of pure CeO 2 irradiated with swift heavy ions. Experimental results showed that the ferromagnetism was induced even at room temperature by 200 MeV Xe ion irradiation. The value of saturation magnetization, M s, systematically changes as a function of ion-fluence. The value of M s increases with increasing the ion-fluence and reaches a maximum value at about the fluence of 2.0 × 10 13/cm 2, and then decreases. The X-ray diffraction (XRD) spectra show that the lattice constant of CeO 2 increases with increasing ion-fluence. This result and our previous XPS result show that the ion-irradiation produced oxygen vacancies. The present study implies that the ferromagnetic behavior of the ion-irradiated CeO 2 is attributed to the magnetic moments of localized 4f electrons on Ce 3+ atoms, which are related to oxygen vacancies. © 2011 Elsevier B.V. All rights reserved.