Abstract: Using 1～2 weeks calf abomasa as material, influences of such factors as ultrasound intensity, extraction time, NaCl concentration, pH value of extraction solution and ratio of abomasum to extraction solution on extracting activity were studied by ultrasound treatment. The experimental results showed that as compared with the traditional method, the ultrasound treatment method resulted in a significant reduction of extraction time and increases in rennet activity. The optimal parameters for the extraction of rennet by ultrasound treatment were as follows: ultrasound intensity 40 W/cm², extraction time 70 min, NaCl concentration 10%, pH value of extraction solution 5.0, the ratio of abomasum to extraction solution 1∶20.