The study presents an investigation of the nanoparticle mixing in discontinuous high shear mixers to measure the limit of mixing quality. The distinguishing feature of these mixers is high circumferential velocity with very high energy input. This property alone enables the dispersal of the two-component mixtures of commercially available nanoparticles under investigation. During the investigations, the question arose as to which measured variables, besides homogeneity, deliver a characteristic criterion for the determination of the mixing time of nanoparticle mixtures. The agglomerate distribution and the fractal dimension will be measured by a transmission electron microscope. The mass concentration of the solid mixture will be assessed by EDX-spectroscopy to obtain the mixing efficiency. The results indicate that the solid mixtures can be influenced significantly by the addition of an additive. The only correct way to characterize mixtures of particular powders is the determination of mass concentration. The other parameters, such as fractal dimension or agglomerate size, are not significant for the determination of the mixing efficiency. (c) 2011 Elsevier B.V. All rights reserved.