The effect of corticosteroid on the diabetic pregnant rats and their fetuses was investigated. Streptozotocin (STB) was injected into the pregnant rats on the fifth day of pregnancy. Dexamethasone (DXM) was injected into the pregnant rats on the 17th, 18th, 19th and 20th days of pregnancy In prenatal rats, the body weight, an abortion rate, number of fetus, the ratio of lecithin/sphingomyelin (L/S) and the levels of blood glucose and phosphatidylglycerol (PG) were determined. In the postnatal rats, the body weight, the levels of blood glucose, fetal number, stillbirth rate, an organ weight and the levels of hepatic glycogen, protein and triglyceride were determined. The body weight of fetuses was lower in the DXM group and higher in the STZ group than the those of control group. Blood glucose of fetuses produced hypoglycemia in the STZ group compared with the control group. A significant increase in the abortion and stillbirth rates was observed in STZ group. The levels of glycogen, protein and triglyceride in fetus liver and the weight of pancreas were significantly increased in the 572 and STZ+DXM groups compared with the control group. The L/S ratio and the level of PG in the amniotic (quid were significantly decreased in STZ group compared with the control group, whereas those of the STZ+DXM group were similar to the control group. It has been observed that corticosteroid administration on the STZ-induced diabetic rats during final stage of pregnancy can prevent the respiratory depression syndrome of neonatal rats.