As applications of nanotechnologies for life and health sciences get booming, magnetic nanovectors undergo a considerable development. Most of the time, such nanovectors are administered to the patients in liquid suspensions by intravenous injection. It is thus crucial to characterize both the collective behaviour and the individual structure of the vectors in liquid suspension. On the other hand their interactions with the targeted regions in the body have to be understood. For this purposes, a multiscale approach of the structure and properties of such nanovectors has been developed, with structural studies carried out through innovative developments based on electron microscopies down to subnanometric resolution and correlated with physical properties.