Objective: This study was undertaken to investigate the effects of antenatal betamethasone and dexamethasone and to determine which is superior for preterm neonates. Materials and Methods: This prospective, randomized, clinical investigation compared the effects of antenatal betamethasone and dexamethasone in neonates born before 37 weeks of gestation between December 20, 2001 and September 10, 2003. Pregnant women with symptoms and signs of preterm labor at 24-34 weeks of gestation or preterm premature rupture of membranes at 24-32 weeks of gestation were randomly divided into two groups receiving either two 12-mg doses of betamethasone given intramuscularly 24 hours apart or four 6-mg doses of dexamethasone given intramuscularly 12 hours apart. We compared the complications of preterm neonates, such as respiratory distress syndrome (RDS), severe intraventricular hemorrhage (IVH), periventricular leukomalacia (PVL), necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP), and neonatal sepsis in the two groups. Results: A total of 140 mothers were included in our study and 157 preterm neonates were surveyed, of whom 81 were exposed to antenatal betamethasone and 76 to antenatal dexamethasone. No significant differences were found between the two groups in the incidence of RDS, severe IVH, PVL, NEC, ROP, and neonatal sepsis. However, compared with a complete course of antenatal corticosteroids, the incidence of RDS was significantly increased after an incomplete course (odds ratio, 2.48; 95% confidence interval, 1.04, 5.93; p = 0.04). Conclusion: In our study, no significant differences between antenatal betamethasone and dexamethasone were found in complications of preterm neonates. Incomplete courses of antenatal corticosteroids were associated with an increased incidence of RDS compared with complete courses.