A lymphangioma is comparatively rare in the elimentary tract, and is a benign tumor of the lymphatic system. A duodenal lymphangioma is especially rare, and has an obscure etiology. Clinically, and in the laboratory the are non-specific, and are incidentally found by endoscopy, and their treatment is total excision. Recently, the authors experienced a 45 year-old woman, who had a duodenal lymphangioma, but with no symptom. An endoscopic examination revealed a single, about 2 cm, polypoid lesion below the ampulla. The lesion was successfully excised after a duodenotomy.