Background: To explore the predictive value of venous cord blood neutrophil-to-lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) for Early-onset sepsis (EOS) in preterm infants. Methods: A prospective cohort of neonates with gestational ages 32 weeks in a single hospital from January 2017 to January 2020 were enrolled. Multivariable logistic regression was used to determine independent risk factors for EOS. ROC curves were created to estimate the predictive capacity. Results: A total of 427 neonates were included in the study. 176 neonates were exposed to chorioamnionitis including 89 EOS and 87 without EOS, and the venous cord blood white blood cell (WBC), (neutrophil) N, (platelet) P, NLR and PLR in the EOS infants were significantly increased. 251 infants were unexposed to chorioamnionitis including 63 EOS and 188 without EOS, and N and NLR were significantly increased in EOS infants. After adjustment for covariates, multivariable logistic regression analysis demonstrated high NLR was independently associated with the subsequent risk of EOS in the infants both exposed and unexposed to chorioamnionitis. The most accurate discriminatory NLR for EOS threshold in infants exposed to chorioamnionitis was 2.68 (AUC = 0.949, sensitivity = 0.839, specificity = 0.933). The most accurate discriminatory NLR for EOS threshold in infants unexposed to chorioamnionitis was 2.01 (AUC = 0.852, sensitivity = 0.830, specificity = 0.762). The cutoff value of the PLR for predicting EOS in the preterm infants exposed to chorioamnionitis was 55.051, the sensitivity was 82%, the specificity was 36.7%, and the AUC was 0.579. Conclusions: Venous cord blood NLR seems to be an early, sensitive and convenient marker for preterm infants with EOS, especially in those exposed to chorioamnionitis. Meanwhile, venous cord blood PLR is not an accurate predictor of EOS in preterm infants.