To date, colonic diverticular bleeding associated with bowel cleansers has not been reported, and its endoscopic and pathological features remain largely unclear. We report a case of colonic diverticular bleeding associated with a bowel cleanser (137 g of polyethylene glycol [NIflec®]) before colonoscopy (CS). CS revealed colonic diverticular bleeding in the sigmoid colon. To our knowledge, this is the first report describing the endoscopic and pathological features of colonic diverticular bleeding associated with bowel cleansing before CS.