<p>Biliary cystadenomas are rare hepatobiliary tumors in cats and are usually characterized by cystic proliferation of the bile duct epithelium. A ten-year-old castrated male British Shorthair cat was brought to the clinic with complaints of abdominal distension and intermittent vomiting. Ultrasound, computed tomography, and magnetic resonance imaging revealed a large, multilocular cystic mass involving multiple hepatic lobes. Hematological and biochemical examinations revealed mild preoperative changes. Postoperative biochemical abnormalities consistent with hepatic dysfunction were observed. Under general anesthesia, resection of the gallbladder, including multiple liver lobes, was performed. Histopathological examination confirmed the diagnosis of biliary cystadenoma. Despite surgical resection and postoperative supportive care, the patient’s general condition deteriorated, and the patient died one week after the operation. This case highlights the diagnostic challenges of distinguishing biliary cystadenomas from malignant hepatic neoplasms and the importance of histopathological evaluation for definitive diagnosis. Furthermore, while surgical resection is the gold standard of treatment, the extent of the lesion and postoperative complications significantly influence prognosis.</p>