This study was carried out to investigate the effect of a scouring machine including an ultrasonic system on desizing and scouring polyester fabrics. The ultrasonic frequency of the improved machine showed up at 28.882 kHz. Frequency amplitude increased with the current and the bath temperature, and then showed a constant level. Scouring effect of the ultrasonic machine was better than that of the conventional scouring machine using the mechanical stirring. The ultrasonic machine showed the optimum scouring effect at $50^circ{C}$ of bath temperature and 10 min. of operation time, as compared to the conventional machine that required operating conditions of high temperature at $90^circ{C}$, stirring speed at 40 rpm, and stirring time for 15 min..