Esophageal carcinosarcoma is a rare malignant esophageal neoplasm consisting of both carcinomatous and sarcomatous elements, with an incidence of 0.5%. There have been only a few case reports of carcinosarcoma and squamous cell carcinoma coexisting in the esophagus. However, all of these are cases of synchronous or metachronous development of carcinosarcoma after chemoradiotherapy in patients of esophageal squamous cell carcinoma. A 53-year-old man underwent esophagogas-troduodenoscopy because of chest pain for several months. Endoscopic examination revealed a huge pedunculated esophageal polypoid mass. Endoscopic submucosal dissection (ESD) was performed and histopathologic examination confirmed spindle cell carcinoma (carcinosarcoma). He refused additional esophagectomy. After 21 months, third follow-up endoscopy showed poorly-demarcated flat, faint discolored lesions at different location from the previous ESD site and endoscopic biopsies confirmed squamous cell carcinoma. To the best of our knowledge, this is the first case of metachronous development of esophageal squamous cell carcinoma in a patient with esophageal carcinosarcoma.