In recent years, cases of diverticular bleeding have become more common. Although identifying the bleeding diverticulum is difficult, it is even more difficult to identify the exposed blood vessels in the bleeding diverticulum. We experienced a case in which we succeeded in directly observing the exposed blood vessels of a sigmoid colon diverticulum using the ultrathin endoscope. The patient was a 71-year-old man who experienced rebleeding after hemostasis in the sigmoid colon by endoscopic band ligation. In the case of diverticular bleeding in the sigmoid colon, we showed that identifying exposed blood vessels by observing the diverticulum under direct vision using the ultrathin endoscope may be useful for hemostasis.