Abstract： Objective To investigate the correlation between the ratio of soluble fms-like tyrosine kinase-1 to placental growth factor(sFlt-1/PLGF)and vitamin D level with disease severity and pregnancy outcome in preg-nant women with late-onset preeclampsia.Methods The clinical data of 121 patients with late-onset preeclampsia who underwent prenatal examination and delivery in Department of Obstetrics and Gynecology,Beijing Anzhen Hospital,Capital Medical University from July 2021 to December 2023 were collected for a retrospective study.According to the severity of the disease,they were divided into severe group(61 cases)and non-severe group(60 cases).After 34 weeks of pregnancy,serum sFlt-1/PLGF and 25-(OH)-D level were measured,and the pregnancy outcomes of the study subjects,including 24 h urine protein levels,gestational weeks of delivery,and newborn weight,were tracked and recorded.Results The serum sFlt-1/PLGF in the severe group was higher than that in the non-severe group[38.20(21.66,69.22)vs 25.59(16.74,51.54)](P＜0.05).The serum 25-(OH)-D level in the severe group was lower than that in the non-severe group(P＞0.05).The serum sFlt-1/PLGF in severe group was negatively correlated with neonatal weight(r=-0.267,P=0.038)and positively correlated with 24 h urine protein level(r=0.377,P=0.003),but not significantly correlated with gestational age at delivery(P=0.645).Conclusion Compared with patients with non-severe preeclampsia,serum sFlt-1/PLGF in patients with severe preeclampsia is significantly higher,but there is no significant difference in serum vitamin D level between the two groups.In addition,serum sFlt-1/PLGF in patients with severe preeclampsia is positively correlated with 24 h urinary protein level and negatively correlated with neonatal weight,suggesting that serum sFlt-1/PLGF may play a role in the prediction of adverse pregnancy outcomes.This study may provide new ideas and methods for early diagnosis and early treatment of preeclampsia.