Objective:To study the preventive and therapeutic effect of N-Acetyl-L-cysteine on infectionassociated preterm labor in mice.Methods:A total of 66 C57BL/6 inbred strain pregnant mice were selected and randomly divided into groups A,B and C,with 22 cases in each group.Group A,B and C were regarded as model group,prevention group and treatment group,respectively.The model of infection-associated preterm labor was built by intraperitoneal injection of Escherichia coli.Ten mice of each group were taken and observed the preterm birth rates and live birth rates,respectively.Three mice of each group were killed at 3 h,6 h,12 h and 24 h after building the model.Their uterus tissues were collected and the expressions of the AP-1 and MCP-1 in those tissues were assayed with immunohistochemical method and the expressions of NF-κ Bp65 and TNF- protein in the placenta tissues of those mice were also detected with immunohistochemical method.Results:The preterm birth rates of mice in groups B and C were significantly lower than that in group A,while their live birth rates were distinctly higher than that in group A(P<0.05);the expressions of the AP-1 and MCP-1 in the uterus tissues and NF-κ Bp65 and TNF- protein in the placenta tissues of mice in groups B and C were evidently lower than those in group A(P<0.05);the comparison of the expressions of the NF-κ Bp65 and TNF- between group B and C showed no statistical differences(P>0.05).Conclusions:N-Acetyl-L-cysteine can lower the incidence rate of infection-associated preterm labor by prohibiting the activation of the protein AP-1/MCP-1and decreasing the expression of NF- κ Bp65 and TNF- in the pregnant tissues of premature mice to reduce the inflammatory reactions. Objective: To study the preventive and therapeutic effect of N-Acetyl-L-cysteine ​​on infection associated preterm labor in mice. Methods: A total of 66 C57BL / 6 inbred strain pregnant mice were selected and randomly divided into groups A, B and C, with 22 cases in each group. Group A, B and C were regarded as model group, prevention group and treatment group, respectively. The model of infection-associated preterm labor was built by intraperitoneal injection of Escherichia coli. Ten mice of each group were taken and observed the preterm birth rates and live birth rates, respectively.Three mice of each group were killed at 3 h, 6 h, 12 h and 24 h after building the model. The uterus tissues were collected and the expressions of the AP- 1 and MCP-1 in these tissues were assayed with immunohistochemical method and the expressions of NF-κBp65 and TNF-protein in the placenta tissues of those mice were also detected with immunohistochemical method. Results: The preterm birth rates of mice in groups B and C were significantly lower than that in group A, while their live birth rates were distinctly higher than that in group A (P <0.05); the expressions of the AP-1 and MCP-I in the uterus tissues and NF- [kappa] Bp65 and TNF - protein in the placenta tissues of mice in groups B and C were evidently lower than those in group A (P <0.05); the comparison of the expressions of the NF-κB p65 and TNF- between group B and C showed no statistical differences (P> 0.05) .Conclusions: N-Acetyl-L-cysteine ​​can lower the incidence rate of infection-associated preterm labor by prohibiting the activation of the protein AP-1 / MCP-1 and decreasing the expression of NF- κ Bp65 and TNF - in the pregnant tissues of premature mice to reduce the inflammatory reactions.