The glucocorticoid dexamethasone has been largely used due to its anti-inflammatory effect. However, several authors report that the excessive exposition to it during pregnancy may cause a retard in the development in several tissues, mainly: liver, lungs and kidneys. But, the majority of the works are done with the application of dexamethasone in the late periods of pregnancy. Because of the lack of researches that evalúate the effects in the beginning of gestation, this paper aimed at evaluating the effect of dexamethasone administered in the initial phase of pregnancy, o ver the morphology of neonates rat. It was used 10 albino rats (Rattus norvegicus albinus) aged 90 days from the lineage Wistar. The female were coupled and divided in two groups: Group I - rats not submitted to the dexamethasone application (control); Group II - rats submitted to the dexamethasone application in the first 5 days of pregnancy. The results show that the treatment with dexamethasone in a dosage of 0.8mg/Kg during the 5 first days of pregnancy does not produces a weight and height reduction or malformation in the offspring, it does not cause changes in the development of the liver and kidneys of neonate rats, but it leads to a reduction in the denseness of the interalveolar septa causing a higher distensión of the alveoli.