Abstract: The utilization of catfish processing by-products were studied in this paper. Crude protease from catfish stomach and intestine were extracted using ultrasonic method. The effects of various factors,including concentration of Na Cl,extraction time,ultrasonic intensity and extraction temperature on protease from catfish stomach and intestine were investigated,respectively. The optimum conditions for the extraction of catfish viscera proteases were obtained by response surface analysis. The results showed that the optimum conditions of pepsin from stomach of catfish were as follows:0.3% Na Cl solution,ultrasonic intensity 90 W,30 min of processing time and at 35 ℃. Under these optimized conditions, the measured protease activity reached130 U/m L. The optimum conditions of protease from intestine of catfish were as follows:0.25% Na Cl solution,ultrasonic intensity 100 W,40 min of processing time and at 35 ℃. Under these optimized conditions,the protease activity reached 114 U/m L. The result indicated that with the same solid to liquid extraction ratio(1∶5),protease from stomach had significantly higher enzyme activity than protease from intestine.