Introduction: Juxtapapillary duodenal diverticulum can cause chronic inflammation of the ampulla, swelling of the nipples, compression of the common bile duct and pancreatic duct openings, and leading to lemmel’s syndrome. Juxtapapillary duodenal diverticulum complicated with lemmel’s syndrome can cause severe signs, such as persistent abdominal pain, cholangitis, pancreatitis, and obstructive jaundice, which is easily confused with other diseases (such as pancreatic tumors and bile duct stones), the rate of misdiagnosis has increased. Therefore, timely identification, diagnosis and treatment to alleviate the symptoms of patients pose certain challenges for clinicians. Case presentation: An 81-year-old patient had a history of hypertension, diabetes mellitus, recurrent pancreatitis, and gallstone disease. Admitted to hospital for half an hour with persistent mid-upper abdominal pain. At that time, we considered that it was caused by choledocholithiasis. However, after preliminary CT examination, a mixed highdensity shadow was found near the descending part of the duodenum, the gallbladder was enlarged and stones were formed, and no choledocholithiasis was found. After admission, abdominal pain was relieved after the treatment of fasting, acid suppression, fluid replacement, and anti-infective, but the next day, abdominal pain recurred, and bilirubin increased significantly. In order to further clarified the cause of this disease, MR cholangiopancreatography was performed, and high density of masses in the descending part of duodenum was found. Dilatation of common bile duct and pancreatic duct, and no choledocholithiasis were found. Due to the patient’s signs were atypical, we were somewhat confused in the diagnosis. After our comprehensive evaluation and discussion, further duodenal endoscopy and tissue biopsy were performed and diagnosed as juxtapapillary duodenal diverticulum, which originated from submucosa. Due to the particularity of this disease and a comprehensive evaluation of the patient, we performed the treatment of EST (Endo-scopicsphincterotomy), and the patient’s symptoms gradually improved after surgery. After follow-up, no obvious abdominal discomfort was found. Discussion and Conclusion: Juxtapapillary duodenal diverticulum complicated with lemmel’s syndrome may not have typical symptoms and specific complications, and the rate of misdiagnosis is high. When patients have symptoms that cannot explain recurrent abdominal pain, bloating, bleeding, and recurrent pancreatitis, the possibility of this disease should be considered, and relevant examinations (such as CT, angiography, and duorectoscope) should be performed in time to identify and diagnose to reduce the incidence of obstructive jaundice and pancreatitis.