Patients who present with nocturnal pain in the left upper abdomen are most likely to have a duodenal ulcer as the cause. Duodenal ulcers are very common in clinical practice and occur for many reasons, such as excessive secretion of gastric acid, Helicobacter pylori infection, decreased defenses of the duodenal mucosa, etc. When abdominal pain occurs in patients, it is usually pain at night or during hunger, which is a more typical abdominal pain characteristic of duodenal ulcer, while patients often have heartburn, acid reflux, bloating, belching and other digestive tract symptoms. Patients are advised to improve routine stool examination and improve gastroscopy to assist in the diagnosis. In addition, some other diseases can also cause nocturnal pain in the upper left abdomen, such as chronic gastritis, gastric ulcer, pancreatic disease, etc. It is recommended that patients seek timely medical attention at the hospital and perform systematic examination to exclude these diseases.