A 10‐year‐old, neutered, male Pitbull was presented to the oncology service with dyspnoea, approximately 16 months after treatment with amputation and chemotherapy for appendicular osteosarcoma, and 4 months after development of diffuse pulmonary metastatic disease. Thoracic radiographs diagnosed bilateral pneumothorax, presumed secondary to metastatic osteosarcoma. The pneumothorax was refractory to conservative management, and two autologous blood patch pleurodesis procedures were performed 48 hours apart, according to a previously published protocol. Marked radiographic improvement was evident within 24 hours of the autologous blood patch pleurodesis procedures, and the dog was discharged 6 days after initial presentation. Approximately 13 weeks later, the dog was humanely euthanased due to progressive clinical signs. This report describes the development of spontaneous persistent pneumothorax secondary to osteosarcoma metastatic disease in a dog, and its palliation with autologous blood patch pleurodesis. This case demonstrates that autologous blood patch pleurodesis can be considered as a treatment option for pneumothorax secondary to metastatic disease in dogs.