Objective:To detect serum levels of placenta growth factor (PLGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) during different periods in normal pregnancy and patients with preeclampsia and to evaluate their role in the pathogenesis of preeclampsia. Methods:Women enrolled prospectively in following groups:healthy pregnant control(n = 200) and preeclampsia patients,who had mild preeclampsia(n = 31) or severe preeclampsia(n = 26) . The serum PLGF and sFlt-1 levels were measured by enzyme linked immunoassay(ELISA). Results:Maternal serum PLGF levels during all periods were significantly lower in the preeclamptic women than in normal controls(P < 0.01). The levels of maternal plasma sFlt-1 were significantly higher in the preeclamptic women than in normal controls during the latter three periods of pregnancy(P < 0.01). The serum sFlt-1/PLGF ratio was significantly higher in the preeclamptic women than in normal controls(P < 0.01). Conclusion:Alterations in the levels of sFlt-1 and free PLGF in maternal serum were associated with the occurrence and development of preeclampsia.