In this study, we tested a hypothesis that a short-term estradiol therapy may reduce blood pressure in preeclampsia by modulating plasma oxidative stress. The intramuscular injections of 10 mg 17-beta-estradiol were prescribed to preeclamptic pregnant women during the 3-day therapy before a labor induction. The analyses of mean arterial pressure (MAP), serum estradiol concentrations, plasma superoxide anion (O₂.), hydrogen peroxide (H₂O₂), nitrites (NO₂⁻), and peroxynitrite (ONOO⁻) were conducted before and during the therapy. We found that the plasma concentrations of oxidative stress markers, such as O₂^– and H₂O₂, are higher in preeclampsia and positively correlated with the MAP value. Moreover, it was shown that the plasma concentration of NO₂^– as an indicator of NO levels is higher in preeclampsia. A short-term intramuscular application of estradiol decreases the MAP value and the plasma concentration of O^.–, H₂O₂, NO₂⁻, and ONOO^– in preeclampsia. A positive correlation between the decrease of MAP values and the decrease of plasma concentrations of O₂^–, H₂O₂, and ONOO^– was found in preeclampsia during a short-term estradiol therapy. We conclude that the short-term estradiol therapy decreases the MAP value in preeclampsia by modulating the plasma oxidative stress. We speculate that the estradiol metabolism in preeclampsia is an important mechanism that contributes to vascular dysfunction.