Backgrounds: In EMR, the physiological saline is usually injected into the submucosa in order to prevent perforation and hemorrhage during complete resection. However, few studies have been reported on the physiological change of submucosal layer by the volume of injected saline. Aim: to assess experimentally the physiological change of submucosal layer after the saline injection on mongrel's surgical specimens. Methods: Fresh surgical specimens were obtained from 3 mongrels' experiments. 3 specimens from the esophagus, 9 from the stomach (fundus, body, and antrum), and 9 from the colon(rectum, transverse colon, and cecum) were used for the experiments. Saline was injected under the mucosa of all specimens on which 1cm sized target areas were made by electrocautery markings from a dose of 1 §¢ to 20§¢. By gross morphology of the elevated area and endoscopic sonographic image on the submucosa of each specimen, the mucosal extension was measured after saline injection. Moreover, histological features of each specimen were assessed after the submucosal injection of saline containing 0.05% methylene blue. Results: In the gross morphology of elevated areas and endoscopic sonographic images, the height of blebs and the minimal diameter of target areas made by saline injection increased up to a fixed dose, but did not increased after that. However, the maximal and minimal diameter of elevated areas and the difference between these diameters increased proportional to the volume of injected saline. Above findings were consistent on all specimens(p>0.05)(Fig 1,2).In histological examininations, retained salines were interspersed evenly among the connective tissues in the submucosa despite the volume of injected saline.Conclusion: Morphological change in the submucosa is not changed proportional to the volume of injected saline, and retained saline is distributed evenly amomg the connective tissue in the submucosa.