An ultrasound method was developed for increased efficiency of chymosin extraction. Ultrasound extraction was carried out with a Tekmar sonic disrupter, and control extraction was by shaking. Use of ultrasound resulted in increase in activity and decrease in nitrogen content, thus increasing the specific activity of chymosin extracts. Proteolytic activity of experimental chymosin was higher at 15 and 20°C, but lower at 35 and 40°C than that of controls. Chymosin extracts obtained by ultrasound treatment were darker, less green, less blue, and more turbid than controls. Ultrasound treatment did not affect activation energies for proteolytic activity, total viable cell counts, or storage stability of chymosin extracts.