Emulsion polymerization using ultrasonic energy has the potential to replace conventional synthetic processes that use chemical initiators. A new polystyrene (PS) latex polymerization process was activated to create radicals and, thereafter, ultrasonic energy was generated by irradiation with a pulse-type horn. The average molecular weight and particle size of the synthetic latex samples were measured using gel permeation chromatography and a particle size analyzer, respectively. The average molecular weight increased with increases in the concentration of surfactant and the ultrasonic energy density. The particle sizes of PS latex were in the range from 45.0 to 73.3 nm at an energy density of 210 J/mL. The particle size also increased, whereas the polydispersity index decreased, as the energy density increased. This data was used to analyze the polydispersity index and the particle size distribution (PSD). The particle size and PSD were both affected by the ultrasonic energy density, the surfactant concentration, and the reaction temperature, with the synthetic processes optimized at 210 J/mL, 1.0 wt% SDS concentration, and 40℃, respectively.