The present work is focused on the characterization of nanoparticles mixing under sound assisted fluidization. In particular, the effects of mixture composition, primary particles density and sound intensity on the mixing quality have been pointed out. The effect of the relative amount of the two powders has been investigated using Al2O3 and Fe2O3 nanopowders and carrying out tests at fixed acoustic field (130 dB-120 Hz) and varying the mixture composition (17,50 and 77 wt% of Fe2O3). Whereas, the effect of nanoparticles density has been studied performing mixing tests between two denser powders, ZrO2 and Cu, at fixed mixture composition (50 wt% of ZrO2) and acoustic field (130 dB-120 Hz), and comparing the results with those obtained with the two lighter powders (Al2O3 and Fe2O3). Moreover, tests between ZrO2 and CuO have also been carried out at different sound intensities (130 and 140 dB), at a fixed frequency and mixture composition, in order to highlight the influence of SPL Both the "global" and the "local" mixing between two different powders have been investigated by means of the Scanning Electron Microscopy with X-ray microanalysis (SEM/EDS) analysis of captured samples, in order to obtain the time dependence of the mixing degree, its asymptotic value and the mixing characteristic time. (C) 2011 Elsevier B.V. All rights reserved.