Congenital infantile fibrosarcoma (CIF) is a rare soft-tissue tumor in the pediatric age group and seldom involves the gastrointestinal tract. A 2-day-old boy was transferred to our hospital with a pneumpoperitoneum. After emergency operation, we could find a solid mass wrapping around a sigmoid colon and performed a segmental resection of sigmoid colon including a mass. Histopathologic examination showed an infantile fibrosarcoma origining from the muscular layer of colon. The baby was discharged on the 17th hospital day and followed for 1 yr without recurrence.