A 65-year-old woman was referred to our hospital for lumbago. The patient was diagnosed with multiple myeloma in 2020. She underwent chemotherapy and radiation therapy, and the disease progression stabilized. In 2022, the patient presented with severe anemia(Hb 4.9 mg/dL), and upper gastrointestinal endoscopy revealed a type 1 tumor in the middle body of the stomach. Computed tomography showed masses in the stomach and pancreas. The patient required a large volume of blood transfusion and underwent total gastrectomy to control the bleeding. Histological examination of the resected specimen indicated infiltration of myeloma cells. The patient died from invasive lesions in other organs, a year after surgery. Usually, extramedullary multiple myeloma lesions occur in the liver, spleen, and lymph nodes. Gastric invasion of multiple myeloma is very rare. Because of poor prognosis, surgery for gastric invasion of multiple myeloma is even rarer. We report a case of gastric invasion of multiple myeloma with a literature review.