Oxide dispersion strengthened steels based on the ferritic/martensitic steel EUROFER97 are developed. The reinforcing particles dispersed in the matrix of EUROFER97 are made of yttria and yttrium titanium oxides. Microstructure is investigated by transmission electron microscopy (TEM). The ODS with yttria presents a tempered martensitic microstructure and a uniform distribution of the yttria. The ODS with yttrium titanium oxide (Y-Ti-O) presents a nano-grained microstructure with a uniform distribution of the Y-Ti-O complex oxides. The microstructure of the yttria particles is investigated by high resolution TEM (HR-TEM). It is found that the dispersed particles made of yttria and Y-Ti oxide are at most semi-coherent with the matrix. The yttria keeps its bcc bulk crystalline structure even after incorporation in EUROFER97. (C) 2009 Published by Elsevier B.V.