Zirconium carbide is one of the candidate materials considered as a component for the fuel elements of some nuclear reactors in the Gen-IV international project. This material has complex bonding and the actual materials have a high vacancy concentration and a non-negligible oxygen substitution on the carbon sub-network. Few data exist regarding its behaviour under irradiation. To study the structural stability of zirconium carbide in the nuclear environment, we have performed low energy ion irradiations (4 MeV An) at room temperature of two different materials, a nearly stoichiometric ZrC0.95 and a ternary ZrC0.85O0.08. Grazing Incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM) were used to monitor the microstructural changes of those materials as a function of the ion fluence. The analyses of the X-ray diffraction diagrams show a moderated swelling, lower for the ternary compound, and high internal strains, both of them saturate at a fluence around 10(14) cm(-2). TEM observations show that the microscopic origin of these strains is mainly due to the formation of a high density of small faulted dislocation loops. As a result, it appears that a high substitution of carbon by oxygen in zirconium carbide does not modify the nature of the defects created under ion irradiation. (C) 2008 Elsevier B.V. All rights reserved.