Pre-eclampsia (PE) is a hypertensive disorder that occurs during pregnancy, and is a multifactorial disease. The antiangiogenic factor, soluble fms-like tyrosine kinase 1 (sFlt-1), has been reported to be important in the pathogenesis of PE, but the mechanism of its involvement remains unknown. To test the effects of sFlt-1 on pregnancy, we injected pregnant mice with exogenous mouse sFlt-1. After 18 days of gestation, higher blood pressure, proteinuria, and histological differences were observed compared with controls. Mitochondrial swelling inside the trophoblast cells in the placenta of sFlt-1-treated pregnant mice was observed by electron microscopy, which suggested a role of sFlt-1 in oxidative stress in trophoblasts in PE. Furthermore, apoptosis markers were upregulated in sFlt-1-treated mice. In conclusion, sFlt-1 appears to play a role in oxidative stress, which promotes apoptosis of trophoblasts. This may be an important mechanism in the development of PE.