Introduction. Citrullus colocynthis Schrad. is a commonly used medicinal plant especially as a hypoglycemic agent. Case Presentation. Four patients with colocynth intoxication are presented. The main clinical feature was acute rectorrhagia preceeded by mucosal diarrhea with tenesmus, which gradually progressed to bloody diarrhea and overt rectorrhagia within 3 to 4 hours. The only colonoscopic observation was mucosal erosion which was completely resolved in follow-up colonoscopy after 14 days. Conclusion. The membranolytic activity of some C. colocynthis ingredients is responsible for the intestinal damage. Patients and herbalists should be acquainted with the proper use and side effects of the herb. Clinicians should also be aware of C. colocynthis as a probable cause of lower GI bleeding in patients with no other suggestive history, especially diabetics.