Ｏｂｊｅｃｔｉｖｅ　To investigate the effects of ulinastatin on extravascular lung water of patients undergoing uniportal video-assisted thoracoscopic unilateral bullectomy under two-lung ventilation.　Methods　Sixty patients (ASAⅠ,Ⅱ) were randomly divided into three groups (n=20): normal saline group (group A), methylprednisolone group (group B) and ulinastatin group (group C). All patients were given intravenous infusion of 100 ml saline (10 ml/min), patients in group B and C received 40 mg methylprednisolone and 500 thousand units ulinastatin respectively. Alveolar-arterial oxygen difference (A-aDO2) and extravascular lung water (EVLW) of all patients immediately before operation (T0) and 10 min after extubation (T1) were recorded. The number of patients with SpO2>95% in different positions and oxygen therapy methods were recorded within 2 h after operation. 　Results　Compared with T0, A-aDO2 and EVLW of all patients at T1 increased significantly. Compared with group A, A-aDO2 and EVLW of patients in group B at T1 were significantly decreased (P<0.05). EVLW of patients in group C at T1 were significantly decreased (P<0.05). Compared with group A in supine position, there are more patients in group B, the difference were statistically significant(P<0.05).　Conclusions　Both ulinastatin and methylprednisolone given by intravenous infusion before operation can significantly decrease the EVLW of patients undergoing uniportal video-assisted thoracoscopic unilateral bullectomy under two-lung ventilation. In comparison, the protective effect of methylprednisolone is stronger than ulinastatin.