To examine the effect of Antenatal corticosteroids (ANS) on the maturation of thyroid function in the preterm infants.ANS reduce mortality and morbidities in preterm neonates. Organ maturation by the glucocorticoids is the key, at least in part. However, the effect of ANS on thyroid are controversial.A study group of 99 very low birthweight neonates (<34 weeks' gestational age) with the exception of those born more than 7 days after ANS administration were divided into a complete group (n = 49) whose mothers completed two doses of betamethasone and who were born more than 24 h after the completion of ANS administration, and an incomplete group (n = 50) who were not exposed to any ANS or were born within 24 h after the completion of ANS administration. Serum free thyroxine and thyroid stimulating hormone (TSH) levels were measured and thyrotropin-releasing hormone (TRH) stimulation tests were performed at about 2 weeks of age.The incidence of hyperthyrotropinemia (TSH > 15 mIU/L) in the complete group was significantly lower than in the incomplete group (6% vs, 22%, P = 0.023). Exaggerated responses to TRH tests were more frequent in the incomplete group (17% vs. 44%; P = 0.053). TSH30 was significantly lower in the complete group, (P = 0.046). Multivariate logistic regression analysis showed that the incidence of hyperthyrotropinemia was associated with complete ANS administration (adjusted odds ratios 0.39).ANS administration might facilitate thyroid maturation in preterm neonates.