Objective:A bioassay called thrombin time(TT) was developed for screening potential thrombin inhibitor and determining anti-thrombin activities of Siwu Decoction and its serial decoctions and some representative compositions.Methods: The lgTT prolongation rate was found to be linearly related to thrombin concentration.The effects of thrombin activities were studied

for example plasma storage methods and time

the chosen of solvent

drug and thrombin pre-heating time.Inhibitory activities of Siwu Decoction and its serial decoctions were compared including Shaofu Zhuyu Decoction(SF)

Xiangfu Siwu Decoction(XF)

Taohong Siwu Decoction(TH)

Qinlian Siwu Decoction(QL).Inhibitory activities of some compositions were determined.Results The suitable condition of optimized bioassay TT is got.Siwu Decoction and its serial decoctions have obvious anti-thrombin activities.Anti-thrombin activities of those decoctions are ranked in the order of QL(IC50=1.30 mg·mL-1)>SF(IC50=1.39 mg·mL-1)> XF(IC50=3.55 mg·mL-1) >SW(IC50=8.14 mg·mL-1)>TH(IC50=10.94 mg·mL-1).Active composition of quercetin also has anti-thrombin activities.Conclusion The optimized method is simple to screen thrombin inhibitor and lays the foundation for compositions of Siwu Decoction and its serial decoctions.