High number density of oxide particles (such as Y2O3, Y2Ti2O7 etc) in oxide dispersion strengthened (ODS) steels provide increased heat resistance of these materials. At the same time investigations with atom probe tomography have shown additional nanoscale clusters enriched with Y, O, V and or Ti. The scope of this study was to understand the influence of heavy ion irradiation on stability of these objects. ODS Eurofer, 13.5Cr ODS and 13.5Cr–0.3Ti ODS steels were irradiated with 5.6 MeV Fe2+ and 4.8 MeV Ti2+ ions up to the fluence of 1015 cm-2. Irradiation experiments were carried out at RT and 573K temperatures. It has been found that in all irradiated specimens number density of nanoscale clusters increased by 2-3 times. In specimens irradiated at 300 K chemical composition of the clusters was altered. At the same time nanoscale features in 13.5Cr–0.3Ti ODS irradiated at 573K remained stable.