Left epigastric subcostal pain with black stool may be caused by gastric ulcer, duodenal ulcer, gastric cancer and other reasons. 1. Gastric ulcer: Gastric ulcer is induced by Helicobacter pylori infection, frequent use of non-steroidal anti-inflammatory drugs, poor dietary habits, etc. Stomach acid stimulates the ulcer surface, causing subcostal pain in the left epigastric region, accompanied by acid reflux, heartburn and other symptoms, and black stools are passed because of the leakage of blood from the ulcer surface. 2. Duodenal ulcer: Due to ulcer in duodenal bulb, exuded blood is discharged into intestine and mixed with feces through bacteria and oxidization in intestine, and black stool will appear, which can be accompanied by pain under ribs in the left upper abdomen, acid reflux, belching (hiccup) and other symptoms. 3. Gastric cancer: invasion of local tissues by cancer cells causes subcostal pain in the upper left abdomen, and bleeding caused by invasion of the tumor site to the surrounding area, because the bleeding location is in the upper gastrointestinal tract, and the blood undergoes oxidation in the intestinal tract, so black stools are excreted. If you have left upper abdomen subcostal pain with black stool, it is recommended to consult doctor in time, do detailed examination, clarify the cause of the disease and treat it as early as possible to avoid delaying the condition.