Objective To explore the impact and possible mechanism of Dahuang Zhechong Wan（ 大黄虫丸）on thrombosis. Methods 1) Fifteen SD rats were randomized into sham operation group

model group

aspirin group

Dahuang Zhechong Wan low and high dose group

3 rats in each group. The Dahuang Zhechong Wan low and high dose group were given 0. 26 and 1. 05 g/（ kg·d） Dahuang Zhechong Wan respectively by gavage. The aspirin group was given 8. 7 mg/（ kg·d） aspirin enteric coated tablet by gavage. The sham operation group and the model group were given 1. 0 g/（ kg·d） normal saline by gavage. All groups were gavaged for 7 days. At 2 hours after the last gavage

rats in other groups except the sham operation group were made common carotid artery thrombosis models. Common carotid artery pathological section was made by hematoxylin and eosin（ HE） stain. 2) Twenty-one SD rats were randomized into blank group

Dahuang Zhechong Wan low and high dose group

7 rats in each group. The Dahuang Zhechong Wan low and high dose group were given 0. 26 and 1. 05 g/（ kg·d） Dahuang Zhechong Wan by gavage. The blank group was given 1. 0 g/（ kg·d） normal saline by gavage. All groups were given gavage for 7 days. At 2 hours after the last gavage

the activity of plasma coagulation factor 11（ FXIa） and the level of Coagulation factor 11 protein（ FXIAg） were detected. The expression of hepatic tissue coagulation factor 11（ FXI） mRNA was detected. 3) Twelve SD rats were given 1. 05 g/（ kg·d） Dahuang Zhechong Wan by gavage for 14 days. The levels of FXIa and FXIAg were detected by heart blood collection on the 0

7 th and 14 th day of medication. Results Pathological results showed that there was no thrombosis in the sham operation group. Rats’ carotid artery was filled with thrombus in the model group. The occlusion degree of carotid artery thrombosis in the Dahuang Zhechong Wan low dose group and in the aspirin group was less severe than that in the model group. Only a small amount of free thrombus was found in rats’ carotid artery in the Dahuang Zhechong Wan high dose group. Plasma FXIa in the Dahuang Zhechong Wan high dose group was less than that in the blank group and the Dahuang Zhechong Wan low dose group（ P < 0. 05）. The difference of plasma FXIAg level and hepatic tissue FXI mRNA level of rats in all groups was not significant（ P > 0. 05）. Compared with the 0 day

rats’ FXIa decreased on the 7 th and the 14 th day.Moreover

the decrease on the 14 th day was more significant than that on the 7 th day（ P < 0. 05 or P < 0. 01）. The difference of rats’ plasma FXIAg level at each time point was not significant（ P > 0. 05）. Conclusion Dahuang Zhechong Wan might have the antithrombotic effect; the mechanism might relate to inhibiting FXIa.