Abstract: Objective　To observe the effects of folic acid on the expression of vascular endothelial growth factor (VEGF) and receptor 1 (Flt1) in placenta of intrauterine growth retardation (IUGR) rats, and the therapeutic effect on fetal development. Methods　Female Wistar rats (n=20) were randomly divided into four groups: the normal control group (N, normal diet), the IUGR group (low protein diet was given during pregnancy), the folic acid + IUGR group (A+IUGR, folic acid 2.0 mg·kg-1·d-1 was given from two weeks before mating to pregnancy, low protein diet was given during pregnancy after successful conception), and the folate + normal control group (A+N, 2.0 mg·kg-1·d-1 folic acid was administered by gavage from 2 weeks before copulation during pregnancy). After successful conception, normal diet was given during pregnancy. Fetal rats were collected by cesarean section at 20 days after pregnancy. Immunohistochemistry, qPCR and Western blot assay were used to detect the mRNA and protein expressions of VEGF and Flt1 in placenta. Results　Compared with the normal group, the fetal body weight, placental mass and placental coefficient were significantly decreased in the IUGR group, and the expression levels of VEGF and Flt1 in placenta were significantly decreased. The placental mass and placental coefficient were significantly increased in the A+IUGR group compared with that of the IUGR group (P＜0.05), and the expression levels of VEGF and Flt1 in placenta were significantly higher in the A+IUGR group than those of the IUGR group (P＜0.05). Conclusion　Folic acid can further improve the placental vascular density by enhancing the expression of VEGF and Flt1 in placenta of IUGR rats, so as to promote the development of placenta and fetal mice, and reducing the adverse pregnancy outcome of IUGR offspring.