Caroli syndrome is characterized by a combination of intrahepatic biliary ductal ectasia and congenital ductal fibrosis due to the failure of involution of ductal plates and large intrahepatic ducts. This study aims to report Caroli syndrome in a dog, with emphasis on clinical characteristics, complementary examinations, and diagnostic approach. A 1-year-old mixed-breed intact male dog was presented with a 7-day history of acute vomiting and anorexia. Clinical evaluation revealed severe jaundice, abdominal pain, dehydration, lethargy, and abdominal distension. Ultrasonography revealed hepatic cysts filled with fluid. Exploratory laparotomy was performed to clarify the imaging findings; however, the dog died shortly after surgery. Postmortem examination revealed that the liver was reduced in size and had multiple interconnected and distended saccular dilations. The bile ducts were markedly dilated and replaced a large part of the liver parenchyma. Multiple small cysts were also observed in the kidneys. Microscopically, the hepatic lesions were characterized by extensive bridging fibrosis associated with proliferating and ectatic bile ducts contiguous with the biliary tree. Marked fibrosis and small cysts were observed in the kidneys. Therefore, a final diagnosis of Caroli syndrome was made. While uncommon, this syndrome should be considered as a differential diagnosis for young dogs with biliary cysts and hepatic fibrosis.