PAR4 antagonist 8 (Compound 20f) is an effective, orally active, and selective PAR4 antagonist with an IC 50 value of 15.32 nM. PAR4 antagonist 8 exhibits favorable pharmacokinetic properties. PAR4 antagonist 8 not only effectively inhibits human platelet aggregation induced by PAR4 agonists ( IC 50 = 6.39 nM) but also inhibits mouse platelet aggregation. PAR4 antagonist 8 can be used in antithrombotic research.