The size reduction by dispersers in the liquid phase was investigated for different energetic materials such as hexogen (RDX), octogen (HMX), 3-nitro-1,2,4-triazole-5-one (NTO), hexanitrostilbene (HNS), ammonium nitrate (AN) and hexamtrohexaazaisowurtzitane (CL20). Two different dispersers, an ultrasonic device and a rotor stator milling device, were used. Changes in the mean particle size and particle size distribution during the comminution could be observed. The use of different ultrasonic intensities for the ultrasonic comminution yields different size reduction results. Induction of ultrasound into a liquid phase was optically investigated in liquids of different viscosity.