Abstract: Objective　To investigate the levels and clinical significance of plasma protein Z (PZ) and protein Z-dependent protease inhibitor (ZPI) during different gestational periods in healthy pregnant women.  Methods　　Fifty cases of healthy non-pregnant women，50 cases of early stage pregnant women (14~27 weeks) and 50 cases of late stage pregnant women (28~40 weeks) were enrolled. Plasma PZ and ZPI were determined by competitive enzyme-linked immunosorbent assay (ELISA). In addition，prothrombin time (PT)，activation partial thromboplastin time (APTT)，thrombin time (TT) and fibrinogen (Fg) content were measured by coagulation method.  Results　The levels of plasma PZ and ZPI decreased gradually from the non-pregnant women to the early stage pregnant women and the late stage pregnant women. Compared to the non-pregnant women，the level of plasma PZ decreased by 16.1%, and the level of ZPI decreased by 22.8% in the late stage pregnant women. Compared to the non-pregnant women，the PT and TT shortened significantly (P＜0.01)，and the Fg increased significantly in the early stage pregnant women and the late stage pregnant women(P＜0.01). Compared to the early stage pregnant women，the PT and TT shortened significantly (P＜0.05)，and the Fg increased significantly in the late stage pregnant women(P＜0.05). Compared to the non-pregnant women，the APTT shortened significantly in the late stage pregnant women (P＜0.05). The decreased levels of PZ and ZPI were related to the shortening of PT.  Conclusions　The activity of blood coagulation factor and coagulation function increase in pregnant women along with the increase of gestational weeks. It may relate to a gradual decrease of the concentrations of plasma anticoagulants such as PZ and ZPI. This kind of physiological change provides a material base for the pregnant women to prepare them to stop bleeding effectively after childbirth，however，it also increases the risk of thrombosis during the pregnancy.

Key words: Protein Z, Protein Z-dependent protease inhibitor, Blood coagulation factor, Pregnancy