Introduction: Adenosquamous carcinoma (ASC) in the stomach is rare. Furthermore, it is even rarer in the remnant stomach. To our knowledge, few case reports related ASC of the remnant stomach have been published to date. The progression of the cancer is extremely rapid, and the prognosis of this condition is generally poor. Case presentation: A 62-year-old Japanese man who underwent a distal gastrectomy with Billroth II anastomosis for a gastroduodenal ulcer 43 years ago was admitted for severe anemia. A gastrointestinal examination revealed a ulcerated tumor at the anastomosis of the gastric remnant. An abdominal computed tomography scan showed gastric wall thickening and no metastatic lesions. He was given a diagnosis of gastric remnant cancer, and he underwent remnant gastrectomy, splenectomy, and lymph nodes resection. Peritoneal cytologicaldiagnosis and lymph node metastasis were positive. The histopathological diagnosis was adenosquamous carcinoma. While the early postoperative course was uneventful, peritoneal dissemination was revealed 3 months later. Conclusion: Although ASC of the remnant stomach is rare, it is aggressive cancers and the patients are poor prognosis. Following patients after gastrectomy on a long-term basis is important to detect cancers in an early stage.