【Abstract】 Objective To observe the effects of Ulinastin against lung injury in patients with septic shock complicating with ALI or ARDS, and explore it’s mechanisms. Methods Eighty-four patients with septic shock complicating with ALI or ARDS were randomly divided into two groups: A group was treatment group(n=42), B group was control group(n=42). All patients in two groups were treated according the Guardlines of rescueing severe septic shock and the Guardlines of the diagnosis and therapy for ALI/ARDS. The patients in group A were received Ulinastatin 200000 Units intravenous once every eight hours and continued for one week in addiction. Parameters of arterial blood gas , oxygenation index(PaO2/FiO2), acute physiology and chronic health evaluation-Ⅱ(APACHE-Ⅱ) score and lung injury Murray’s score were measured respectively on 1 st, 3 rd, 5 th, 7 th day, the rate of MODS and mortality were calculated in one week. Results In comparison with control group , PaO2, PaO2/FiO2 , APACHE-Ⅱscore and the rate of MODS were improved obviously（p<0.05），lung injury Murray’s score and mortality didn’t decreased obviously（p >0.05）in treatment group . Conclusion Tryspin inhibitors--Ulinastatin can mitigate lung injury , protect lung function , and reduce the occurrence of MODS in patients with septic shock complicating with ALI or ARDS.