This investigation shows that ozagrel, an antithrombotic drug, can inhibit mushroom tyrosinase well. The IC50 value was 3.45 mmol/L. Ozagrel was estimated to be a reversible mixed-type inhibitor of mushroom tyrosinase by Lineweaver-Burk plots. The inhibition kinetics has been studied by using the kinetic method of the substrate reaction described by Tsou. The constants of tyrosinase and tyrosinase-substrate complex inhibited by 1.0 mmol/L ozagrel have been determined to be 87.28 and 66.07 µmol/L, respectively.