Dynamic light scattering (DLS) was applied to the study of the process of the preparation of de-aggregated water suspensions of alumina nanopowders with specific surface area 20–140 m2/g. Nanopowders were prepared by the electric explosion of wire and laser evaporation, and accordingto electron microscopy (TEM) consisted of non-agglomerated spherical nanoparticles with lognormal size distribution. According to DLS, non-sedimenting water suspensions of alumina nanoparticles, stabilized by sodium citrate at 5 mM concentration, contain substantial fraction of aggregates. The dynamics of the change of the mean average size of aggregates under the exhaustive ultra-sound treatment of suspensions with 10 g/l concentration for1.5–4 hours by two types of ultra-sonic processors was studied. It was shown that the mean average size of aggregates exponentially diminishes by 1.5–2 times and the fraction of individual particles in suspension enlarges from 45 to 85 %. The sequential centrifuging of the suspension at 18000 g provides separation of the remaining aggregates and results in preparation of the suspensions of individual alumina nanoparticles. Particle size distributions in these suspensions obtained by TEM and DLS are the same within experimental error.