Primary duodenal adenocarcinoma is a rare disease, and cases with nodal metastases have a poor prognosis. A 46-year-old man complaining of bloody stool visited our hospital. Endoscopy, CT, and PET-CT showed adenocarcinoma in the 2nd portion of the duodenum. We performed radical resection (PpPD) and pathological findings showed T3N1M0 (Stage III). Chemotherapy consisting of FOLFOX6 was administered for 6 months after surgery. The patient was alive without recurrence 5 years later. This case suggests that adjuvant chemotherapy (FOLFOX regimen) following curative resection including lymph node removal is an effective treatment for cases with tumor involvement of the lymph nodes.