Ammonium perchlorate (AP)‐based composite propellant is the most widely used solid propellant. Fine AP is required to obtain a propellant with a high burning rate. To prepare fine AP, an emulsion was prepared by emulsifying toluene and the AP solution. The emulsion was frozen rapidly with liquid nitrogen and then freeze‐dried. Fine AP was prepared by this freeze‐drying method. In this study, the emulsion was prepared with the premixer adopted dual‐sonic technology and an attempt was made to prepare finer AP. By using a dual‐sonic premixer, the emulsion was efficiently prepared, and therefore, a fine AP sample was obtained, compared with the homogenizer that is commonly used. It was found that the AP sample could be used as a propellant oxidizer according to its impact and thermal sensitivities.