Objective: To investigate the association between maternal apolipoprotein A-1 (ApoA-1), apolipoprotein B (ApoB), ApoB/ApoA-1ratio and preterm birth (PTB). Design: Observational survey. Setting: Guangdong Women and Children Hospital, China Samples: 5986 pregnant women. Method: Data were extracted from the information system of Guangdong Women and Children Hospital. Maternal serum ApoB, ApoA-1 and ApoB/ApoA-1 ratio were categorized into tertiles. Logistic regression models were performed to evaluate the odds ratios and 95% confidence intervals for PTB. Main outcome measures: PTB (gestational age < 37 weeks) Results: Of the study participants, the rate of preterm birth was 5.7% (n= 344). Compare with individuals in the lowest tertile, the adjusted ORs of PTB was 1.41 (95% CI: 1.07-1.87) for individuals in the highest tertile of ApoB and 1.35 (95% CI: 1.03-1.78) for those in the highest tertile of ApoB/ApoA-1. The association of ApoB/ApoA-1 and PTB was more relevant among women with pre-pregnancy BMI ≤ 24 kg/m2, age at delivery ≥ 35 years or those who were multiparous. Conclusions: Elevated maternal ApoB level and ApoB/ApoA-1 ratio during mid-pregnancy were related to increased risk of PTB. Monitoring serum apolipoprotein levels may help to prevent preterm birth. Funding: The study was funded by grants 2019FYH003 from Chinese Center for Disease Control and Prevention. Keywords: Apolipoprotein A-1, Apolipoprotein B, Apolipoprotein B/Apolipoprotein A-1, Preterm birth Tweetable abstract：Maternal mid-pregnancy ApoB level and ApoB/ApoA-1 ratio were associated with PTB.