Amniotic fluid (AF) may induce disseminated intravascular coagulation (DIC) when it enters maternal circulation by breaching the placental-maternal circulation barrier. The precise mechanism of the procoagulant activity of AF is unclear, but tissue factor (TF) has been proposed to be the main cause. As one constituent of AF, AF cells accumulate and undergo apoptosis continuously. Therefore, we speculate that AF cells have procoagulant activity due to the externalisation of phosphatidylserine (PS). The present study aims to demonstrate that, in addition to TF, the PS that is externalised on AF cells is important for the procoagulant activity of AF. Ten AF samples from parturient women were analysed using lactadherin as the probe for PS. Anti-TF antibody also was used to identify TF and its associated coagulation functions in AF cells. Normal platelets, neutrophils, and lymphocytes were harvested as controls. Confocal microscopy and flow cytometry was used to assess PS expression on AF cells. The procoagulant activity of AF cells was demonstrated by a plasma coagulation assay and further confirmed by factor Xase/prothrombinase assays. PS and TF were present on most AF cells, providing substantial procoagulant activity. Furthermore, factor Xase and prothrombinase assays showed that AF cells substantially enforced the activation of factor X and prothrombin. PS on AF cells is an important procoagulant source for AF. Lactadherin is an ideal anticoagulant for inhibiting the procoagulant activity of AF cells.