In this study, ultrasound-assisted extraction method (UAE) was developed to obtain the protease-rich extract from sheep abomasum (SAE). UAE parameters were first optimized using response surface methodology. Ultrasonic time of 18 min, ultrasonic power of 260 W, and a liquid/solid ratio of 22 mL/g resulted in the highest proteolytic activity and yield of the SAE (4,951.3 U/g, 14.3%, respectively). Then we investigated SAE's gastroprotective effect against gastric ulcers induced by water immersion-restraint stress in rats. After 7 days of intragastric administration of the SAE (0.2 g/kg/day), the ulcer index (2.710.97; p<.05) decreased significantly compared with that in the model group, and the ulcer inhibition ratio was 66.5%. In addition, the response to stress was significantly attenuated by balancing the levels of norepinephrine, 5-hydroxytryptamine, and dopamine in brain regions. Sheep abomasum is the main waste of the sheep meat industry. Converting those wastes to value-added products would be beneficial for both environment and economy. Results of this study presented that UAE resulted in a higher proteolytic activity and yield of SAE with a shorter extraction time than the conventional extraction method. The SAE obtained in this study may be a promising agent for prophylaxis and treatment of stress-induced ulcers.