Background/Aims: Since the risk of cancer cells seeding the peritoneum after perforation during endoscopic submucosal dissection (ESD) is unclear, we retrospectively examined peritoneal relapse after gastric perforation during ESD for gastric cancer at a single institution. Methods: Of 876 patients who underwent ESD for early gastric cancer between January 2002 and December 2015, 22 patients (2.5%) experienced gastric perforation during ESD at the Osaka National Hospital in Osaka, Japan. Clinical data from these 22 patients were reviewed for information on pathology, clinical course, and evidence of peritoneal dissemination. Results: Patients were followed for a median of 55 (range 2–108) months. Two patients had peritoneal seeding following perforation during ESD. Multivariate analysis to explore the influence of clinical factors on the peritoneal seeding revealed that an intra-abdominal fluid collection on the CT imaging just after ESD, tumor location at the upper lesion of stomach, and pathologically marginal invasion were independently associated with an incidence of peritoneal relapse. Conclusion: Although rare, we should recognize the possibility of cancer cells seeding the peritoneum after perforation during gastric ESD.