Abstract： Objective To investigate apoptosis of placental syncytiotrophoblast in patients with early-onset and late-onset severe preeclampsia. Methods From November 2008 to May 2009, 15 cases with early-onset severe preeclampsia and 15 cases with late-onset severe preeclampsia matched with 10 women with normal pregnancies as control at Sixth Affiliated Hospital of Shanghai Jiaotong University were enrolled in this study. Enzyme-linked immunosorbent assay was used to measure syncytiotrophoblast microparticles (STBM) levels in peripheral venous plasma. Caspase-3 were measured by western blotting.Results (1)STBM: the level of STBM of (71 ± 21 )μg/L in early-onset group were significantly higher than (42 ±30)μg/L in late-onset group and (26 ± 11)μg/L in control group(P ＜0.05). The level of STBM in late-onset group and control group did not reach statistical difference ( P ＞ 0. 05 ). ( 2 ) Caspase-3:the level of caspase-3 protein were 0. 85 ± 0. 61 in early-onset group and 0. 77 ± 0. 46 in late-onset group,which were all significantly higher than 0. 32 ± 0. 15 in control group( P ＜ 0. 05 ). However, the level of caspase-3 protein in early-onset group did not show remarkable difference compared with that in late-onset group (P＞0. 05). Conclusion STBM are shed into the maternal circulation in higher amounts in earlyonset preeclampsia, which indicated that early-onset and late-onset severe preeclampsia may have different etiology and pathogenesis.