Despite the increasing interest in preterm birth risk associated with maternal exposure to the current level of fine particulate matter (PM 2.5) in Korea, there is little information on differences in PM 2.5 exposure and its impact on preterm birth. This study was designed to examine the effects of Korea's air quality on preterm birth, including the possibility of moderation and mediation. This work was also designed to investigate manipulable factors for PM2.5 exposure. The theoretical framework of this quantitative and observational study included the social ecological theory and systems theory. The conceptual framework of this partially ecologic and retrospective cohort study included the social ecological model and Rothman's sufficient component cause model. Data of 19,371 Korean women who gave birth in 2015 were analyzed by logistic regression and multiple regression, including testing for moderation and mediation. An increase in PM2.5 exposure by 10 microg/m3 in the 3rd week before childbirth increased the likelihood of preterm birth by 6.52 times. Moderation and mediation by PM2.5 did not exist between sociodemographic factors and gestational age but existed between socioeconomic and energy policy factors and gestational age. The most influential factor for PM2.5 exposure was unemployment rate at the organizational level. These results show the need for socioeconomic interventions to reduce PM 2.5 exposure more effectively. These findings indicate that prenatal care should be addressed with a socioeconomic- and energy-policy-sensitive approach to lower preterm birth due to severe air pollution in Korea. This study has the potential to change people's perceptions of threats from PM 2.5 exposure, which could lead to behavior changes.