We report a case of endocrine cell carcinoma in the sigmoid colon with inferior mesenteric vein (IMV) tumor embolism. A 79-year-old woman was admitted to our hospital with narrowing of the stools. We performed colonoscopy, computed tomography and positron emission tomography, which disclosed sigmoid colon cancer with IMV tumor embolism. She underwent sigmoidectomy and lymph node dissection. The tumor was diagnosed as endocrine cell carcinoma (type 4, pSS, med, INFα, v3, n1, stage chromographin A, synaptophysin, cytokeratin 20 and mucicarmine showed partial staining, and CD56 was totally reactive. Three months after operation multiple liver metastases appeared. She was treated with chemotherapy of cisplatin (CDDP) + irinotecan (CPT11). This case highlights the aggressiveness of endocrine cell carcinoma with tumor embolism, and it is essential to establish an accurate diagnosis and effective treatment. We report a case of endocrine cell carcinoma in the sigmoid colon with inferior mesenteric vein (IMV) tumor embolism. A 79-year-old woman was admitted to our hospital with narrowing of the stools. We performed colonoscopy, computed tomography and positron emission tomography The tumor was diagnosed as endocrine cell carcinoma (type 4, pSS, med, INFα, v3, n1, stage chromographin A, synaptophysin, cytokeratin 20 and She was treated with chemotherapy of cisplatin (CDDP) + irinotecan (CPT11). This case highlights the aggressiveness of endocrine cell carcinoma with tumor embolism, and It is essential to establish an accurate diagnosis and effective treatment.