Radioembolization with yttrium-90 (Y90) is a recent oncological interventional radiology technique used to treat hepatocellular carcinoma and metastatic colon cancer to the liver. Although Y90 selective internal radiation therapy (Y90-SIRT) is considered a safe and effective treatment, with increasing use, hepatic and extrahepatic complications have been reported. Here, we present a case of upper gastrointestinal bleeding caused by gastric ulceration associated with radioembolization from Y90-SIRT, as confirmed by histological findings. Unlike dyspeptic ulcers, radioembolization ulcers originate on the serosal surface, predisposing patients to adhesions, bowel obstruction, or perforation, as well as gastrointestinal bleeding.