We investigated whether the use of antenatal corticosteroids could improve the maturation of choroid plexus capillaries in fetal mice. The study was carried out in two groups of preterm mice. The study group consisted of pregnant mice that received dexamethasone at a dose of 4 mg/kg intraperitoneally. This group was further subdivided into four subgroups according to the timing of steroid administration as follows: day 13, day 14, day 15, and day 16 of pregnancy, and each subgroup included 12 premature mice. All animals received a second injection 24 hours after the first injection. The control group was given normal saline. The pregnant mice were operated on to obtain premature mice. The choroid plexus capillaries were assessed for integrity and thickness of their basement membranes by electronmicroscopy. We found that, in the study group, the maturity of the basement membrane of the choroid plexus capillaries was more precise, in that capillaries were better in control animals at term for the following reasons: (a) the basement membrane becomes more intact, (b) thickness of the basement membrane increased, and (c) the protein particles become tighter. Antenatal dexamethasone improved the maturation of the choroid plexus capillaries in fetal mice but also decreased the incidence of periventricular–intraventricular hemorrhage (PIVH). Using two doses of steroids had no influence on birthweight or brainweight of the mice. In conclusion, these findings provide an experimental basis for the use of antenatal steroids for decreasing the incidence of PIVH in premature infants.