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Introduction Hepatitis B virus (HBV) has recently been reported to impair both sperm and oocyte function, potentially increasing infertility and birth defects risks, although primarily recognised as a concern for mother-to-child transmission. Population-based evidence regarding the association between paternal preconception HBV infection and preterm birth (PTB) risk is absent.Methods This retrospective cohort study was conducted based on the National Free Preconception Checkups Project between 22 April 2010 and 31 December 2020 in China. Paternal preconception HBV infection statuses were divided into three groups: uninfected, past exposure and immunity, and current infection. Inverse probability weighting (IPW) via propensity models was used to adjust for imbalance by different groups of paternal preconception HBV infection status. Log-binomial regression models were employed to estimate the relative risk ratios (RRs) of PTB associated with paternal preconception HBV infection.Results 7 395 829 couples were included, with a PTB incidence of 5.65%. Compared with HBV-uninfected males, those with prior HBV exposure had a 5% increased PTB risk in offspring (RR 1.05, 95% CI 1.04 to 1.07), and those infected with HBV currently showed a 10% increased PTB risk (RR 1.10, 95% CI 1.09 to 1.12). No significant association was observed when both partners had the same HBV immunity prior to pregnancy (RR 1.01, 95% CI 0.99 to 1.03). Moreover, an interaction effect between maternal and paternal preconception HBV infection was observed ( Pfor interaction=0.003), with couples both currently infected with HBV showing the highest PTB risk (RR 1.16, 95% CI 1.11 to 1.20). Consistent results were obtained across all PTB subtypes.Conclusions Both paternal current HBV infection and prior exposure were identified to be associated with increased PTB risks independently. Moreover, the interaction impact of HBV infections between couples on PTB risks should also be considered. These findings provide new evidence for the paternal risk factors of PTB, highlighting the importance of comprehensive HBV screening and immunity management for both parents before conception to reduce PTB risks.