Contents Diabetic diarrhea is seen mainly in patients with poorly controlled diabetes patients. Typically, the diarrhea is painless, occurs during the day and night, and may be associated with fecal incontinence. Ramosetron, a selective 5-HT3 receptor antagonist, which was developed as an antiemetic in cancer chemotherapy, is useful in the treatment of diarrhea in patients with irritable bowel stndrome. The efficacy of ramosetron in the treatment of diabetic diarrhea has been documented,but the cases were all male poorly uncontrolled patients. We report a case that a 72-year-old female with refractory diabetic diarrhea was successfully treated with ramosetron. A 72-year-old female was admitted in our hospital due to severe diarrhea. She had poorly controlled diabetes, orthostatic hypotension, diabetic retinopathy, nephropathy, peripheral neuropathy, autonomic neuropathy and gastroparesis. She was prescribed on conventional antidiarrheal agents, including a pancreatic enzyme supplement, probiotics, cimetropium bromide and loperamide, but these were ineffective. Coloscopy was performed the result was normal. She was thus diagnosed with diabetic diarrhea and treated with ramosetron 5 μg once daily. Diarrhea completely disappeared after 1 week and recurred right away after cessation of ramosetron.