A 7-year-old Thoroughbred gelding was admitted to Equine Hospital, Korea Racing Association for evaluation and treatment of colic. Based on the size and duration of the large colonic and cecal impaction, a routine ventral midline celiotomy and large colon enterotomy were performed to relieve the impaction. Six days following surgery the gelding exhibited signs of lethargy, fever, inappetence and diarrhea. Eleven days following surgery, the jugular veins showed a marked thrombophlebitis. On the sixteenth day of hospitalization the gelding died suddenly. Upon physical examination, the horse was febrile, tachycardic and tachypnoeic. Thoracic excursion appeared to be increased; however, no abnormal lung sounds were detected. No cough or nasal discharge was present. Hematology revealed neutrophilic leukocytosis. Serum biochemistry was normal but plasma fibrinogen increased. In necropsy, fibrinopurulent fluid was present in the thoracic cavity. There were firm adhesions between visceral pleura and thoracic wall. White, mixed and red thrombi were formed in both jugular veins from the insertion point of IV catheter. Histopathological examination showed fibrinopurulent inflammation and vascular thrombosis in the lung. The pleura showed edematous thickening and severe congestion. The clinicopathological and pathological findings suggest that septic thrombi associated with septic thrombophlebitis metastasized into the pulmonary circulation and were entrapped in the pulmonary parenchyma and provoked pleuropneumonia.