Gastrointestinal malignant fibrous histiocytomas (MFH) are very rare and only about 30 cases have been reported in the English literature, among which 20 cases were from colorectal MFHs. A small bowel MFH with intussusception has been the only reported case in the Korean medical literature. A 52-year-old male presented with complaints of recently developed and aggravated right upper abdominal pain. We present the CT appearance and the clinico-pathologic findings of his primary inflammatory malignant fibrous histiocytoma, which arose from the subserosal layer of the ascending colon with tumor infiltration in all the layers. The colon showed extensive hemorrhagic necrosis and repetitive multifocal microperforations with resultant panperitonitis.