Reported herein is an unusual case of carcinosarcoma of the colon. A 13-year-old girl was transferred to Chonbuk National University Hospital, Korea with a known pelvic mass. CT and magnetic resonance imaging confirmed a large pelvic mass. A sarcoma was diagnosed following colonoscopic biopsy. An ultra-low anterior resection with pelvic lymph node dissection was performed. The tumor consisted of a well-differentiated adenocarcinoma showing strong immunoreactivity to epithelial markers (pancytokeratin, cytokeratin 7, cytokeratin 19, cytokeratin 20, epithelial membrane antigen, and CEA) and a sarcomatous lesion with strong diffuse vimentin expression but no immunoreactivity to any of the six epithelial markers. Carcinosarcomas of the colon are extremely rare, and all reported cases involve adults. To the authors' knowledge, this is the first reported case of a carcinosarcoma of the colon in a child.