Over the last few years, oxide dispersion strengthened (ODS) ferritic steels have emerged as one of the major materials for fusion reactors. Despite the progress made in their technology, currently available properties still do not meet all the expectations. As a result these steels remain the subject of extensive research, recently centred on a possible improvement due to their nanometric engineering. In particular, technologies are developed for grain size refinement down to nanometres and strengthening by nanooxides. This, in turn, calls for nanoscale investigations of the microstructures, which can be efficiently carried out only with the use of high-resolution transmission electron microscopy and spectroscopy. The present paper illustrates the results of investigations of a model alloy of ODS steel using a recent high-resolution scanning transmission electron microscope equipped with a spherical abberation Cs-correction system, energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy spectrometers. It allows bright field on transmitted electron imaging and secondary electron imaging, as well as high-angle annular dark field imaging, the so-called Z-contrast imaging. The results obtained in dark field prove that modern microscopy techniques are a necessity to provide new information on the nanostructure of the ODS steels relevant to the understanding and shaping of their properties.