Donor lung thrombi are considered an important etiology for primary graft dysfunction in lung transplantation. This study was designed to evaluate the effect of the fibrinolytic agent plasmin on lungs damaged by thrombi in an ex vivo lung perfusion (EVLP).(Study 1) Rats were divided into the sham, control, and plasmin groups (n = 7, each). In the control and plasmin groups, cardiac arrest was induced by withdrawal of mechanical ventilation without heparinization. After 150 min warm ischemia, the lungs were excised and perfused in the EVLP system for 60 min, and plasmin or placebo was administered upon EVLP initiation. (Study 2) Rats were divided into three groups: the sham (n=5), control (n=7) and plasmin (n=7) group. After 120 min warm ischemia, the lungs in the control and plasmin groups were administered plasmin or placebo at the initiation of EVLP and assessed. Finally all rats in each group were perfused with heparinized rat blood.(Study 1) FDP in the perfusate were significantly higher in the plasmin group than those in the sham and control groups (p < 0.001, both). Plasmin administration significantly decreased pulmonary vascular resistance (p = 0.011) and inhibited the exacerbation of dynamic compliance (p = 0.003). Lung weight gain was less in the plasmin group than in the control group (p = 0.04). In the plasmin group, residual red blood cells were significantly fewer than those in the control group. (Study 2) Physiological data of reperfusion period reflected the results of study 1. Lung oxygenation was significantly better in the plasmin group than that in the control group throughout the entire reperfusion period (p < 0.001, each). TUNEL staining revealed that more apoptotic cells were seen in the control group than in the plasmin and sham groups.Our results confirmed that plasmin administration in an EVLP model dissolved thrombi in the lungs, resulting in reconditioning of the lungs as assessed by various physiological parameters.