Most cases of diarrhea with black stools are due to two causes: 1) acute inflammatory infections leading to increased diarrhea symptoms; 2) irritable bowel syndrome or inflammatory bowel disease leading to chronic enteritis. Acute enteritis is often due to viral or bacterial infections, resulting in congestion, edema and erosion of the intestinal mucosa, and erosion can easily lead to bleeding, and the blood, after metabolism by intestinal bacteria, turns from trivalent iron ions to divalent iron ions and causes the characteristic of black stools. Chronic enteritis or ulcerative colitis is often accompanied by mucus-purulent stools or mucus without pus-blood due to surface ulceration, which causes local breakdown leading to bleeding. The repeated occurrence of diarrhea with black stools suggests perfecting routine stool examination, routine blood examination, and if necessary, perfecting colonoscopy to further clarify the diagnosis.