Various risk factors are associated with neonatal sepsis; however, its relationship to maternal postpartum fever is unknown. This study aimed to determine the relationship between maternal postpartum fever and neonatal sepsis. Full-term and late preterm stable infants born from January 2019 to June 2021 and whose mothers developed intra- or post-partum fever were included in the study. After the newborns were transferred to the nursery, laboratory assessments were performed. Based on clinical conditions and data, the newborns were divided into unlikely sepsis and probable/proven sepsis groups. Maternal fever onset, duration, and maximum body temperature were recorded. We included 1059 newborns whose mothers developed fever intra-partum (n = 192), post-partum (n = 844), and intra- and post-partum (n = 23). The newborns were grouped into those with unlikely sepsis (n = 550) and those with probable/proven sepsis (n = 509). The incidence of intrapartum fever was higher in the probable/proven sepsis group than in the unlikely sepsis group (27.9% vs. 13.3%, p < 0.001). The incidence of postpartum fever was lower in the probable/proven sepsis group than in the unlikely sepsis group (74.7% vs. 88.5%, p < 0.001). Development of maternal fever within 1.8 h postpartum and a newborn respiratory rate of >60 breaths/min were positive predictors (91.6%) for neonatal probable/proven sepsis.