Preterm birth is a global concern with considerable morbidity and mortality. Intrapartum infection is a known cause of preterm birth and Actinomyces infection is one of the infections contributing to preterm birth. We report a case of preterm birth of a trisomy-21 neonate to a mother with positive Actinomyces naeslundii from an intra-operative placental swab sample and discussed the relationship of this bacteria and preterm delivery, and the role of postpartum antibiotics use in this case.