We describe herein the case of a 54-year-old Japanese woman in whom an inveterate peptic ulcer developed in association with pseudo-Zollinger-Ellison Syndrome (pseudo-ZES). The patient presented with weight loss and abdominal distension caused by antral and duodenal stenosis due to an inveterate peptic ulcer. Her serum gastrin level was very high; however, no evidence of a gastrinoma or carcinoid tumor was detected by preoperative examinations or surgery. A total gastrectomy and double-tract reconstruction was performed, and pathological examination revealed a gastric ulcer (UL-IV) with no histopathological evidence of a neoplasm. Immunohistochemical staining showed an obvious increase in the number of endocrine cells that were positive for chromogranin A, and marked G-cell hyperplasia was observed in the antral mucosa. Furthermore, the number of enterochromaffin-like cells was remarkably high. From the results of the immunohistochemical examination, the patient was diagnosed as having hypergastrinemia due to antral G-cell hyperplasia. Postoperatively, the patient's serum gastrin level fell rapidly to within the normal range, her nutritional status improved, and her weight increased by about 10 kg within 1 year.