The accessory hepatic lobe is an extremely rare anomaly reported in humans and animals. A large domed solid mass and two smaller masses were noticed during thorax dissection in a six-year-old mixed breed male dog with no previous history of the disease, which was fixed to be used in the anatomy hall. The masses were placed adjacent to the diaphragm, between the lung's right and left caudal lobs. The masses with a common thick vascular pedicle had pierced the diaphragm and run to the falciform ligament of the liver. Histological findings showed liver tissue and hepatocytes were arranged radially around the central vein. There were sinusoids between the hepatocyte plates, dilated as telangiectasia in some areas. The study of the pedicle revealed a normal elastic artery, normal vein, and normal biliary duct crossed to the falciform ligament in the abdomen. The macroscopic and microscopic findings revealed type I intrathoracic ectopic liver.