Carcinoid tumors are slow growing neoplasms that arise from enterochromaffin cells, with malignant potential, and those of the duodenum are rare neoplasms, with an incidence of 2.0~8.9% of all gastrointestinal carcinoid tumors. Duodenal carcinoid tumors rarely manifest gastrointestinal symptoms and carcinoid syndrome. A healthy 43 year old woman was admitted due to an incidentally detected duodenal mass during regular health screening. An abdominal CT scan and UGI series showed a polypoid mass at the second portion of the duodenum without bowel dilatation. The duodenoscopic finding was a carcinoid tumor, which was proven by immunohistochemical staining. A pylorus- preserving pancreatoduodenectomy was performed and a 2.5x2.2 cm sized submucosal tumor found at the second portion of the duodenum, with two periduodenal lymph node enlargements. Immunohistochemical staining showed that the tumor cells to have positive reaction for NSE, chromogranin and synaptophysin. Herein, our experience of a malignant duodenal carcinoid tumor is reported.