A hydrocyclone for collecting micron-sized hydrosols efficiently has been studied through experimentation. Hydrocyclones separate particles of the dispersed phase from the liquid on the basis of the density difference between the phases. The purpose of this study was to design and evaluate the performance of a high-capacity hydrocyclone for the removal of submicron-sized particles suspended in liquid. Furthermore, the performance of three types of hydrocyclone was evaluated with regard to solid particle density using fly ash and coagulation sludge. The particle cut-size decreases with reducing inlet area and increasing inlet velocity in the hydrocyclone. The hydrocyclones have good performance, which is demonstrated by the optimal cut-size of 20 μm in mass median diameter at the inlet diameter per body diameter ratio of 0.21 and the pressure drop of 72.5 kPa with a particle density of 2,500 kg/m3.