Powder mixing is a typical operation in particle technology. This work presents a method for the determination of the homogeneity of dry nanoparticle powder mixtures to measure the limit of mixing quality. The research results given here reflect the experimental effort required to study nanoscale solid mixtures consisting of a two-component system of Aerosil 200 and the titanium dioxide additive P25. The experimental effort can be evaluated by means of statistical methods. The parameter measured is the so-called homogeneity or mixing efficiency. It is determined by means of an energy-dispersive X-ray spectroscopy detector attached to a transmission electron microscope. The results will show that the optimal homogeneity depends on the additive concentration, the magnification of the transmission electron microscope, and the number of agglomerates, which have to be analyzed.