Abstract: Objective To explore anticoagulant effect of total diterpenoids extracted with ethanol from Isodon japonica(Burm.f.) Hara var.glaucocalyx(Maxim.) Hara in mice.Methods A total of 90 mice were randomly divided into blank control group,positive drug group,and high,medium,low dose total diterpenoids groups.The different treatments were conducted with gavage administration once a day for 7 days.Tail transection and capillary glass tube method were used to determine clotting time(CT) and bleeding time(BT).Results The CT was 425.00±13.32 seconds and 559±36.17 seconds for the mice treated with high dose total diterpenoids extracted with heating reflux and cold soak method,respectively,and significantly longer than that of the blank control(201.00±18.52 seconds).The BT was 3308.00±271.33 seconds and 3758.00±184.53 seconds for the mice treated with high dose total diterpenoids extracted with heating reflux and cold soak method,respectively,and significantly longer than that of blank control(2094.00±58.59 seconds).Conclusion Total diterpenoids extrated from Isodon japonica(Burm.f.) Hara var.glaucocalyx(Maxim.) Hara could extend capillary blood coagulation time and tail bleeding time and has anticoagulant effect in mice.