The ischemic colitis occurring proximal to obstructive colon cancer is a rare case, which has the prevalence ranging 1% to 7% of the colon cancer. The pathogenesis is unclear but it is thought that raised intraluminal pressure, distension and bacterial stasis in the partially obstructive bowel play a role in developement of ischemia. The ischemic damage of colon is usually localized and reversible. However we experienced a case of extensive gangrenous ischemic colitis associated with rectal cancer in 48- year-old man, and he developed acute abdominal symptom and needed prompt surgical operation. So we reports this case with a review of literature. (Korean J Gastrointest Endosc 2004;28:321325)