A fibrosarcoma is a malignant mesenchymal tumor derived from fibrous connective tissue. It usually develops in the deep soft tissues of the extremities, as well as the trunk, head, and neck. In extremely rare cases, a fibrosarcoma may occur in the gastrointestinal tract. Most cases of fibrosarcoma in the gastrointestinal tract have been observed in the pediatric age group while only a few cases have been reported in adults. A 61-year-old male presented with pain in the entire abdominal region. Chest radiography showed free air in the subphrenic space. After an emergency operation, we found a solid mass around the transverse colon and performed a segmental resection with a lymphatic dissection of the transverse colon, including the mass. A pathologic examination showed a fibrosarcoma with a perforation. There was no perioperative complication. The patient was discharged on postoperative day 11 and had follow-ups for 1 year without any recurrence.