We performed left lung retransplantation on 5 mongrel dogs, 3 dogs died peroperatively because of hemoragie and hypoventilation. The other two lived 7 and 4 days. There were not any complication on arterial and bronchial anastomosis on postmortem examination. However, there were large thrombosis formation in left atrium on both dogs. Thrombosis formation which is seen most commonly after lung retransplantation caused postoperative mortality in this study.