A 57-year-old man who was diagnosed with a gastrointestinal perforation during a plain abdominal CT scan performed to evaluate an acute abdomen and was urgently transferred to our hospital. The duodenal bulb had extensive ulceration and perforation in the anterior wall during the upper gastrointestinal endoscopy. Consequently, a laparoscopic-assisted closure of the perforation was performed with the round ligament of the liver. On postoperative day 5, the patient developed shock with massive melena. An urgent upper gastrointestinal endoscopy revealed a gastroduodenal artery pseudoaneurysm at the base of the ulcer on the posterior wall of the duodenum. After marking the duodenal mucosa adjacent to the pseudoaneurysm with a clip, the patient was taken to the angiography suite. Angiography revealed that pseudoaneurysm of the gastroduodenal artery was identified at the site corresponding to the clip, and hemostasis was achieved through coil embolization. The patient was discharged without any further bleeding, and the ulcer was healed on endoscopy two months later. We report a case of rupture of a pseudoaneurysm of the gastroduodenal artery into the duodenum after surgical closure of a perforated duodenal ulcer.