Influence of the non-cavitational powerful ultrasonic action (PUA) on the particle size distribution and lattice parameters of crystallites of zirconia and alumina dry nanopowders have been studied. The ultrasonic treatment occurred into the acoustic waveguide having a cavity, filled by dry nanostructured powder (NP). The PUA of different power was used to various dry NP: ZrO2-8%Y2O3 (TZ-8Y, TOSOH); ZrO2-3%Y2O3 (TZ-3YS, TOSOH); ZrO2-3%Y2O3 (PCZY, Siberian Chemical Plant, SCP); Al2O3 (UDPO, SCP). It was found that non-cavitational PUA influences the lattice parameters and average agglomerate sizes of dry zirconia and alumina NP. There are extreme PUA powers at which extreme values of the lattice parameters and average agglomerate sizes are correlated. The crystal structure of the TZ-3Y (synthesis by spray-drying) is more stable against PUA than PCZY (plasma-chemical synthesis).