This study focused on the effects of ultrasound on emulsification and enhancement of the synthesis of monodispersed fine particles of the conducting polymer polypyrrole by chemical oxidative polymerization. Monodispersed polypyrrole particles were synthesized in water by chemical oxidative polymerization with ultrasonic irradiation under conditions of low oxidant concentration and room temperature, and the effects of ultrasonic frequency on the morphology of synthesized polypyrrole particles and polymer yield were investigated. Polymer yield with ultrasound was larger than that without ultrasonic irradiation for the same reaction time, and ultrasound promoted the polymerization. At frequencies of high sonochemical efficiency, the average particle size decreased and the polymer yield increased. On the other hand, at the frequency of low sonochemical efficiency of 20 kHz, the polymerization reaction was enhanced and polymer yield increased.