It has been well recognized that antenatal administration of dexamethasone to pregnant women at risk of preterm delivery may significantly accelerate fetal maturation and reduce the risk of adverse perinatal outcomes in their preterm infants, particularly for births before 34 weeks of gestation. Since 2015, antenatal corticosteroid administration has been extended beyond 34 weeks of gestation by clinical guidelines, as it might have beneficial effects on fetal maturation and perinatal outcomes. However, concerns regarding the potential influence of antenatal corticosteroid treatment on offspring neurodevelopment have been raised. This study aimed to investigate whether maternal antenatal corticosteroid administration was associated with neurodevelopment in infants at 1 year of age. In this prospective and longitudinal birth cohort study, women were followed up throughout gestation, and their infants underwent a Bayley Scales of Infant and Toddler Development, third edition, screening test at 1 year of age between December 2018 and September 2020. Finally, 1609 pregnant women and 1759 infants were included in the current study. Using a generalized linear mixed model, we examined the association between antenatal corticosteroid exposure and infant neurodevelopment in cognitive, receptive communication, expressive communication, fine motor, and gross motor functions. Of the 1759 infants eligible for this study, 1453 (82.6%) were singletons. A total of 710 infants were exposed to antenatal corticosteroids, among whom 415 were dexamethasone-exposed and 483 were prednisone-exposed. Dexamethasone was prescribed most often in late pregnancy while prednisone was often used before 8 weeks of gestation among women who conceived through assisted reproductive technology. Compared with those who had no exposure, antenatal corticosteroid exposure was associated with an increased risk of infants being noncompetent in the cognitive development domain after adjusting for conventional risk factors (adjusted risk ratio, 1.53; 95% confidence interval, 1.08-2.18; P=.017). For medication-specific exposure, those exposed versus not exposed to antenatal dexamethasone were 1.62-fold (95% confidence interval, 1.10-2.38; P=.014) more likely to be noncompetent in the cognitive development domain at 1 year. The association did not vary significantly between preterm and term infants, singletons and twins, or assisted-reproductive-technology- and spontaneously conceived infants (all P >.05 for heterogeneity). In contrast, a null association was observed for the risk of being noncompetent in any domain of neurodevelopment with antenatal prednisone exposure at early pregnancy. In this cohort study, antenatal corticosteroid, particularly dexamethasone exposure, was significantly associated with an increased risk of infants being noncompetent in the cognitive development domain at 1 year of age. These findings may provide new information when weighing the benefits and potential risks of maternal antenatal corticosteroid administration.