The paper presents and compares two methods for the synthesis of fine particles of the high explosives HNS and HMX by ultrasonic treatment and solvent/antisolvent crystallization. The effect of ultrasonic treatment on the particle size of explosives was studied by varying the amplitude and frequency of ultrasonication for different time periods using an ultrasonic probe and an ultrasonic bath. Solvent/antisolvent recrystallization was performed by varying the process parameters including stirring rate, antisolvent temperature etc. In addition to FT-IR spectroscopy and thermal analysis by TGA/DSC; the particle size and shape of fine powders of the explosives HMX and HNS were determined using particle size analysis and scanning electron microscopy (SEM). Ultrasonic treatment of the probes resulted in the finer grains of HMX compared to solvent-antisolvent crystallization. However in the case of HNS, solvent-antisolvent crystallization produced finer particles compared to ultrasonication.