Objective:To investigate effects of prenatal single-dose administration of dexamethasone and ambroxol on pulmonary morphology of fetal and neonate rats. Methods:Thirty-six pregnant rats were randomly assigned to two groups:the treatment group (n=9) and the control group (n=9). On day 17 of pregnancy,the rats in the treatment group were injected intraperitoneally with dexamethasone and ambroxol,while the rats in the control group were injected intraperitoneally with equivalent volumes of isotonic saline. The histologic structures of lungs of each group were observed with light microscope and trans-mission electron microscope on day 19 of pregnancy,postnatal days 3 and 7,respectively. The differences of pulmonary morphogenesis between two groups on different periods were studied. Results:(1) Under the light microscope:lungs in the treatment group had more alveolar numbers (P < 0.05),larger alveolar space (P < 0.01),and thinner alveolar septum (P < 0.01) compared with the control group on day 19 of pregnancy;lungs in the treatment group had larger alveolar space (P < 0.05),thinner alveolar septum (P < 0.05),while alveolar numbers had no significant difference (P > 0.05) compared with the control group on postnatal day 3;lungs in the treatment group had larger alveolar space (P < 0.05),thinner alveolar septum (P < 0.05),while alveolar numbers had no significant difference (P > 0.05) compared with the control group on postnatal day 7;(2) Under the electronic microscope:villi of type Ⅱ alveolar epithelial cells in the treatment group were denser and more integral than those in the control group;the lamellar body could be seen in the treatment group while hardly in the control group on day 19 of pregnancy. There were many lamellar bodies in both groups,while lamellar bodies in the treatment group were more anachromasis and condensed compared with the control group on the postnatal 3 days and 7 days. There were also many cellular organs such as bioblast in endochylema of the treatment group on the postnatal 3 days and 7 days. Conclusion:Prenatal single-dose administration of dexamethasone and ambroxol can promote lung maturation not only of fetal rats but also of neonate rats,without obvious harmful effects.