We present a case of long-term survival in primary malignant lymphoma of the duodenum treated with a curative surgical resection and post-operative chemotherapy. A 72 year-old man was admitted to our hospital complaining of epigastric discomfort. Endoscopy revealed an ulcerative tumor in the duodenal bulb. The tumor was diagnosed histologically as malignant lymphoma by endoscopic biopsy. A distal gastrectomy and duodenal bulb resection were performed with lymph nodes dissection. The tumor was histologically classified as B-cell phenotype, large cell, immunoblastic lymphoma of high grade, according to the Working Formulation. The patient received CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone) chemotherapy after the operation, and he has no sign of recurrence during a follow-up period of 6 years.