Pulmonary sequestration is a rare congenital anomaly in the veterinary literature. This malformation is characterized by a cystic mass of non-functioning primitive lung tissue that does not communicate with the tracheobronchial tree or with the pulmonary arteries. This article describes gross and histopathological characteristics of extralobar pulmonary sequestration in a dog. Grossly, a mass was observed in the left side of the thoracic cavity, closed to the caudal lobes of the lung, without communication with the tracheobronchial tree and the pulmonary arteries that was separated by pleural covering. Histopathologic examination showed emphysematous alveoli and bronchi, hypertrophy of smooth muscles and presence of the undifferentiated mesenchymal tissue. Therefore, based on microscopic findings, extralobar pulmonary sequestration was diagnosed. To the best of our knowledge, this is the first report of extralobar pulmonary sequestration in dog.