The bile samples were obtained from the gall bladder as well as from the common bile duct of the human and the dog, and the effect on the coagulation of rabbit's blood was studied. The gall bladder bile inhibited blood clotting so strongly that no clotting was observed within 24 hrs. Although the hepatic bile showed a similar action, the extent of inhibition was much weaker than that of the gall bladder bile. On the other hand, the white bile obtained from a patient had no effect on blood clotting. On the basis of these findings, it was thought that either bilirubin or cholate in bile is responsible for delaying blood dotting. However, bilirubin had no effect while taurocholate or desoxycholate delayed blood clotting considerably, indicating that cholate is responsible for the anticoagulant action of bile. Further studies indicated that taurocholate has strong antithrombin as well as antiprothrombin activities. However, the fibrinolytic activity of taurocholate was not detected. On the basis of these results, it is concluded that bile salts, especially tallrocholate or desoxycholate, are responsible for delaying blood clotting by counteracting the activities of thrombin and protilronlbin.