A 63-year-old man was seen at the hospital because of heart burn, bloody stool and abdominal fullness. After close examination, a left upper abdominal mass was diagnosed as mesenchymal tumor arising from the transverse mesocolon, which involved the transverse colon, stomach and jejunum. Enbloc resection of the huge tumor mesuring 16×12×9cm was performed. There was a 9×8cm type 3 tumor on the mucosa of the transverse colon. The tumor was diagnosed as neuroendocrine carcinoma of the transverse colon pathologically with immunohistochemical stains. He died of multiple liver metastases three months after the operation.