0.1 % of hospitalized patients are attributed to upper gastrointestinal bleeding every year in the U.S. and Europe, among which peptic ulcer is the most common cause of upper gastrointestinal bleeding. Endoscopic hemostasis procedure in the management of bleeding due to peptic ulcers was safe as well as effective and lowered recurrent bleeding, surgery and mortality. Endoscopic treatment is widely used as an effective and safe method but it has disadvantages including the need for the endoscopy specialist and the likelihood of developing the complications such as perforation or recurrent bleeding although they rarely occur. Thus, less invasive medical treatments with fewer side effects have been continuously studied and among them, gastric acid inhibitors have been studied the most.Acid and pepsin inhibit platelet aggregation, activation of blood coagulation system, and fibrinogen polymerization. Blood clots already formed are digested by pepsin and the activity of pepsin is closely related to intragastric pH level. Therefore, it is known that an elevated intragastric pH facilitates hemostasis process, induces hemostasis by stabilizing hematoma and prevents recurrent bleeding. To suffice these conditions, it is reported that a potent gastric acid inhibitor is needed to maintain intragastric pH of 6 or higher.