Acute pulmonary edema affects 0.08% to 1.5% of women during pregnancy and during the postpartum period, and preeclampsia/eclampsia is a major obstetric cause of acute pulmonary edema. We present a case of a 23-year-old nulliparous woman who was referred totertiary medical center for preterm labor and dyspnea (Mousavi Hospital). The patient complained of having suddenly developed respiratory distress and a decrease in O2saturation following the administration of magnesium sulfate. A chest radiograph taken at bedside showed widespread interstitial shadowing consistent with pulmonary edema. The patient was given prompt treatment, and she achieved full recovery. Pharmacological agents are one of the defendants used for lung edema during pregnancy. It is important to pay attention to lung edema due to tocolytic administration.