Abstract: OBJECTIVE To observe the expression levels of IL-21, TNF-α and MMP-9 in serum of rats with lung injury induced by intrauterine infection. METHODS Healthy SD rats during pregnancy were randomly divided into the control group and lipopolysaccharide（LPS） group. The LPS group was divided into 6 concentration groups of 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 mg/kg, respectively. LPS solution of different concentrations were intraperitoneally injected on the 18 th day of pregnancy, while the control group was intraperitoneally injected with the same volume of sterile normal saline. The abortion rate and fetal mortality during pregnancy were recorded. The lung tissue damage of neonatal rats was observed by hematoxylin-eosin HE staining. The serum levels of IL-21, TNF-α and MMP-9 in neonatal rats were detected by enzyme-linked immunosorbent assay（ELISA）. RESULTS Compared with the control group, neonatal rats in the LPS group had significant inflammatory damage in their lung tissues. Compared with the control group, the mortality rate in the LPS group was significantly higher（P＜0.05）. With the increase of LPS concentration, the mortality rate of neonatal mice was gradually increased, and the difference among all groups was significant（P＜0.05）. The serum levels of IL-21, TNF-α and MMP-9 in neonatal rats in the LPS group were significantly higher than those in the control group（P＜0.05）. The serum levels of IL-21, TNF-α and MMP-9 were gradually increased with the increase of LPS concentration, and the differences among all groups were significant（P＜0.05）. CONCLUSION Intrauterine infection model can be successfully established by intraperitoneal injection of LPS into rats during pregnancy. Intrauterine infection can cause increased mortality and lung tissue damage of neonatal rats. Meanwhile, the expression levels of IL-21, TNF-α and MMP-9 in serum of neonatal rats in the LPS group were increased in a dose-dependent manner.