We aimed to evaluate antithrombotic efficacy of Protaetia brevitarsis extract during 21 days. Rats (SPF rat, weight 240~260 g) were divided into 16 groups (5 rats per group), they were: control group and Protaetia brevitarsis extract groups with dose of 0.1, 0.5, 1, 2.5, 5, 10, 25, 50, 75, 100, 200, 250, 500, 750, 1,000 mg/kg kg of body weight. Thromboplastin time (PT) and activated partial thromboplastin time (aPPT) as antithrombotic efficacy were tested in this animal experiment (at 7, 14 and 21 days). Overall, the admistration dose of Protaetia brevitarsis extract over 50 mg/kg at 7, 14 and 21 days for PT and over 25 mg/kg at 7, 14 and 21 days for aPPT tented to be longer than that of other groups. In addition, the optimal admistration doses of Protaetia brevitarsis extract to improves antithrombotic efficacy were 75, 100, 200 and 250 mg/kg at 7, 14 and 21 days for PT (p<0.05) and 50 and 100 mg/kg at 7 days, 75 mg/kg at 14 days, or 50, 100, 200 and 250 mg/kg at 21 days for aPPT (p<0.05). It can be concluded that Protaetia brevitarsis extract at optimal levels have antithrombotic efficacy.