Spherical ammonium nitrate particles with average diameters of 82-206 mu m were produced using the melt spray system built in the present work The effects of spray pressure and temperature on the size distribution and average diameter of the ammonium nitrate particles were investigated It was found that increasing the spray pressure at given temperature or increasing the temperature at given pressure enhanced the disintegration of the front edge of the liquid sheet into fine droplets and, thus, slightly reduced the average diameter of the ammonium nitrate particles X-ray diffraction patterns confirmed all spherical ammonium nitrate particles to be form IV because of a rapid phase transition from form I to form IV Dombrowski and Johns' equation, which is applicable to highly viscous spray fluids, was found to be satisfactory for estimating the Sauter diameter of the ammonium nitrate particles