A 74-year-old male was admitted to Sendai Saiseikai Hospital with a complaint of upper abdominal pain. Gastrointestinal fibroscopy showed type 2 gastric cancer in the lower third of the stomach,and distal gastrectomy and D 2 lymph node dissection were performed. Metastatic lymph node 8 a had severely infiltrated the pancreas, and pancreatoduodenectomy was required to complete the curative surgery. However, because of preoperative complications of interstitial pneumonia, metastatic node 8 a remained untreated. Postoperatively, radiation therapy (38 Gy plus a boost of 18 Gy) for residual lymph node metastasis was performed over a one-month period. The metastatic node underwent complete regression following radiation therapy, and the patient was discharged without any adverse effects. He received TS-1 medication as postoperative adjuvant therapy. Four years have passed since the complete regression of the lymph node,and the patient has shown no signs of relapse. Therefore, our case suggests that postoperative radiation therapy can be a useful tool for treatment of residual lymph node metastasis in gastric cancer.