Nanoparticles, whose size is 1-100 nm, easily aggregate as their size becomes smaller. Therefore, it is difficult to produce solution in which nanoparticles are dispersed. We have, as a way to disperse aggregated particles, for example, a media-typed disperse machine. During the procedures, however, we have to deal with some complicating operations; separation of the media from the solution, the defacement of the media into the solution, and so on. Furthermore, it is not an effective method for particles whose size is less than 50 nm. We tried to find an easier and more effective method for producing solution in which we re-disperse aggregated nanoparticles to still smaller particles. The aggregated particles were put into a machine with a pinhole small needle valve, and they were re-dispersed by "sheering stress". The estimation of re-dispersion was carried out by the measurement of their size distribution and surface z-average. With the utility of the machine, the re-dispersions of aggregated particles were observed. Furthermore, the increase of the pressure and of the velocity of the flow caused the decrease of particle size, which makes the surface area larger and therefore the surface z-average larger. It become clear that it is possible to re-disperse aggregated nanoparticles by adding shearing stress. We can regulate shearing stress by controlling the pressure and flow, and therefore we can control the effectiveness and the yield.