Objective：The goal of this study is to explore the effects of ulinastatin on acute lung injury in fetal rat induced by fetal distress，and provide support for developing a new treatment of respiratory distress syndrome. Methods：A total of 16 SD pregnant rats were randomly divided into four groups：the control group（group C），the ulinastatin control group（group S），the fetal distress group（group A），and the ulinastatin treatment group（group U）. Group C and group S were sham operation groups. Fetal rat intrauterine distress model was set up in both group A and group U. Thirty minutes before the operations，the pregnant rats in group S and group U received injection of ulinastatin 50 000 U/kg through femoral vein. Five living fetal rats were removed in each pregnant rat. The blood gas analysis and the lung wet / dry weight ratio（W/D）of fetal rats were determined. The pathological changes in the lung tissue of fetal rats were observed by H＆E staining，and the protein expression of NF-κB p65 were measured by Western blot. Furthermore，the levels of TNF-α and IL-6 in the fetal lung were measured by ELISA. Results：All the results in group S had no significant difference with group C（P >0.05）. The pH value and partial pressure of oxygen were significantly lower in group A than group C，and those in group U were obviously higher than group A（P＜0.05）. The partial pressure of carbon dioxide，lactic acid content，the lung W/D，and the protein expression of NF-κB p65，the levels of TNF-α and IL-6 of fetal rats were all significantly increased in group A than group C（P＜0.05），and those in group U were obviously lower than those in group A（P＜0.05）. The congestion and edema of the lung tissue in group U were obviously alleviated than that of group A. Conclusion：Ulinastatin can alleviate the degree of acute lung injury in fetal rat induced by fetal distress by decreasing the protein expression of NF-κB p65，the levels of TNF-α and IL-6，inhibiting the inflammatory response and increasing the partial pressure of oxygen.