A 67-year-old man with a history of esophageal and gastric varices that were treated endoscopically was treated for Budd-Chiari syndrome and immunoglobulin G4-related sclerosing cholangitis in our facility. Varices in the second portion of the duodenum were revealed in follow-up upper endoscopy. The draining vein formed a venous plexus that was detected on computed tomography. Treatment with interventional radiology was difficult;therefore, endoscopic injection sclerotherapy (EIS) was performed instead. No recurrence has been observed to date. Thus, in this case, EIS for duodenal varices was effective.