Abstract: Objective To investigate the association between maternal serum neutrophil-lymphocyte ratio (NLR) and placental inflammatory response (PIR) in late pregnancy. Methods We retrospectively analyzed the clinical and follow-up data of 478 pregnant women undergoing routine prenatal examination and delivery in our hospital in the year 2016. According to the placental pathological results, the women were divided into PIR group (238 cases) and control group (240 cases). The levels of serum inflammatory makers including leukocytes, neutrophils, lymphocytes, C-reactive protein (CRP) and NLR were compared between the two groups to analyze the association of these markers with PIR. Multivariate analysis was performed to identify the independent risk factors of PIR. Logistic regression model was established and the area under the receiver operating characteristic curve (ROC) was used for analyzing the prognostic value of these makers in late pregnancy. Results The areas under the curve (AUC) of leukocytes, neutrophils, lymphocytes, CRP and NLR were 0.698 (95%CI: 0.485-0.766), 0.716 (95%CI: 0.453-0.783), 0.329 (95%CI: 0.228-0.431), 0.725 (95%CI: 0.677-0.765) and 0.801 (95%CI: 0.742-0.856), respectively. After adjusting the confounders, multivariate logistic regression analysis showed that preterm labor (OR=2.446, 95%CI: 1.003-4.590), premature rupture of membranes (OR=2.304, 95%CI: 1.049-4.161), NLR>7 (OR=3.268, 95%CI: 2.071-6.920), and CRP>15 mg/L (OR=2.137, 95%CI: 1.412- 8.236) were independent risk factors for PIR. Conclusion An increased NLR in late pregnancy can serve as an effective indicator for predicting the risk of PIR.