Blood coagulation occurs when blood comes in contact with artificial materials. Therefore, during extracorporeal circulation in hemodialysis, open heart surgery using artificial cardiopulmonary device, etc., anticoagulant such as heparin is administered to blood to prevent coagulation. However, the risks of side effects increase with excessive dosage of heparin. The risks of side effects of heparin may decrease with the decreasing dose of heparin following ultrasonic wave irradiation. However, it is not clear whether the anticoagulation effect of anticoagulants on blood increases with ultrasonic wave irradiation. Thus, in the present study, the changes in activated coagulation time (ACT) of human blood with ultrasonic wave irradiation were measured and the use of ultrasonic wave irradiation to decrease the dose of heparin was evaluated. The results demonstrated that ACT decreased with 0.33 U/mL heparin, but increased with 1.30, 1.99, 2.49, and 3.13 U/mL heparin, following ultrasonic wave irradiation at 130 kHz and 20 W. However, the ratio of ACT of blood subjected to ultrasonic wave irradiation to that of control blood was constant at heparin concentration of >1.30 U/mL. In addition, hemolysis and ultrasonic wave irradiation to heparin did not induce heparin-concentration-dependent changes in ACT. Taken together, the vibration of heparin and/or heparin-AT III complex by ultrasonic wave irradiation was suggested to be a possible mechanism for the heparin-concentration-dependent changes in ACT.