Oxide dispersion strengthened-reduced activation ferritic martensitic (ODS-RAFM) steels are foreseen as future structural materials for the ITER and DEMO fusion reactors. Microstructure characterisation experiments of these steels were performed in the initial normalized and tempered condition and after long term annealing. Two types of ODS steel samples were studied. Long term annealing of the samples was performed at 700 °C during 5000 h in ambient atmosphere. Samples were analysed by nuclear microprobe techniques before and after the long term annealing experiments and data compared. The uneven yttrium distribution found in the as-received samples produced by one of the suppliers (20 50 mum Y depleted zones) could not be observed after the long term annealing. This same sample presented significant surface alterations that extend up to 120 mum. The other sample showed a smaller surface alteration (˜30 mum) and the formation of Cr-rich clusters 7 10 mum wide.