Ischemic colitis still remains largely underdiagnosed despite the fact that it is one of the most common disorders of the large bowel. The aims of the present study were to evaluate the variable histologic findings of ischemic colitis and to find out helpful histopathological features in diagnosis. Retrospective review of the clinical symptoms, underlying diseases, endoscopic findings of 23 patients, and the histologic features of 37 biopsies was done. We analyzed the significant pathologic features in the histologically diagnosed ischemic colitis group and compared the biopsy time between the histologically diagnosed ischemic colitis group and the non-diagnosed group. Comparison of the endoscopic biopsy time between the group that showed significant histologic features and the group that showed no significant histologic features was also done. The age of the patients ranged from 27 to 87 years. Most patients had abdominal pain, hematemesis, and melena. Endoscopic differential diagnoses included ischemic colitis, ulcerative colitis, infectious colitis, tuberculous colitis, Crohn's disease, and pseudomembranous colitis. Histologic features and diagnoses were also variable. The coagulative necrosis of mucosa and the epithelial desquamation were frequently detected in the group pathologically diagnosed as ischemic colitis. The most pathognomonic finding was coagulative necrosis of the mucosa that was almost always detected within seven days after the onset of clinical symptoms. Recognition of variable patterns of ischemic colitis in a biopsy specimen will direct the clinician to evaluate the vascular system. Early endoscopic biopsy is essential for the precise diagnosis of ischemic colitis.