Abstract: Objective: To observe the therapeutic effect of ulinastatin on acute lung injury/acute respiratory distress syndrome(ALI/ARDS).Methods: Thirty-four patients with ALI/ARDS were randomly divided into treatment group(n=17) and control group(n=17).The control group received only the routine therapy,and the treatment group were given ulinastatin(200 ku intravenously,once every 8 hours,and continued for 10 days) in addition to the routine treatment.The efficacy was assessed in both groups.The parameters of heart rate,respiratory rate,oxygenation,average arterial blood pressure and arterial blood gas were monitored.Serum levels of tumor necrosis factor-α(TNF-α),interleukin-1(IL-1) and IL-6 were measured on admission,the day 4 and the day 7 in both groups.Results: Before treatment,the TNF-α,IL-1 and IL-6 levels were not significantly different between the ulinastatin group and the control group(P>0.05);but descended significantly after treatment in the ulinastatin group(P<0.01),as well as the respiratory rate,heart rate,and the average arterial blood pressure.The blood gas analysis proved that PaO₂ and PaO₂/FiO₂ increased significantly in the treatment group compared with those in the comparison group(P<0.01).Conclusions: Ulinastatin may significantly inhibit the production of inflammatory cytokinases and thus prevent the systemic injury by inflammatory response and improve the prognosis of ALI/ARDS.