Ischemic colitis is the consequence of a sudden reduction in colon blood supply, which in turn results in ischemic injury. The splenic flexure and rectosigmoid junction are the areas most often affected. Ischemic colitis occurs with greater frequency in the elderly and is caused by various medications and procedures. Pseudoephedrine acts as a vasoconstrictor directly affecting adrenal receptors of nasal mucous membrane. Pseudoephedrine occasionally causes vascular insufficiency due to intense vasoconstriction, even at standard doses. Ischemic colitis associated with pseudoephedrine has been reported in other countries,, but it has never been reported in Korea. In this paper, we describe 3 cases of ischemic colitis that occurred after taking pseudoephedrine for nasal congestion.