The aim of this study was to compare in vivo effects of single and repetitive doses of betamethasone (BETA) and dexamethasone (DEX) administered to pregnant mice on lung maturation and lung, liver, and body weights (LLBW) of their pups. One hundred and eighty gravid Swiss albino mice were randomly assigned to 1 of 6 groups (n = 30) and administered either BETA, DEX, or saline as a single dose at 14 d gestation or repetitive doses twice daily at 14 and 15 d gestation. All the study groups were then divided into three sets (n = 10). The mice in the second sets were redivided into three subsets randomly (including four, three, and three mice). All gestations in the first sets were terminated at 16.5 d gestation to observe the neonatal breathing pattern (scale to 0-5; 5 is unlabored breathing) of male and female pups whereas other sets had normal delivery. The pups in first, second, and third sets were killed for evaluation in the first set after the evaluation of breathing pattern, in the subsets of second set on postnatal d 1, 3, and 5, and in the third set on postnatal d 90. We recorded maternal body weights at 0 and 16.5 d gestation, and LLBW, the lung/body weight ratio of pups, sex, and the amount of live and dead births per litter. Pups exposed to BETA and DEX had significantly lower maternal weight compared with the saline groups. The death litter size was significantly higher in pups exposed to repetitive doses of DEX than the other treatments. Sex had no significant effect on breathing score and LLBW. Pups exposed to repetitive doses of BETA and DEX presented a higher breathing score than the other groups. The breathing score was significantly higher with BETA than DEX after their repetitive use. The LLBW were significantly less in the treatment groups, especially in the group exposed to repetitive doses of DEX. In conclusion, repetitive doses of BETA and DEX lead to increased fetal lung maturation, but this may be at the expense of fetal and neonatal growth. DEX is less potent in accelerating lung maturation than BETA but it causes more reduction in fetal and neonatal growth.