A 90-year-old man was diagnosed with primary gastric diffuse large B-cell lymphoma (PGDLBL) by PET/CT examination, gastroscopy, biopsy and histopathological analysis at a regular physical check in April, 2016. The patient received R-CO chemotherapy (rituximab, cyclophosphamide, and vincristine) and radiotherapy subsequently, with enteral nutritional treatment through 3-cavity nasogastric tube due to development of pyloric obstruction. To satisfy patient's strong desire of eating by himself, we performed surgery of exploratory laparotomy and Roux-en-Y gastric bypass (RGB) to relieve pylorus obstruction. Postoperatively, the patient resumed oral feeding, supplemented by nasogastric tube feeding at 1350 - 1550 Kcal daily. He is now 94 years old with fairly well nutrition and normal communication. The outcome of 4 year follow-up suggests that nutritional treatment and palliative medicine are important for improving prognosis and life-quality of very elderly patients with end-stage tumors apart from the effective chemotherapy, radiotherapy, and surgery.