The inhibition kinetics of alkylbenzoic acids on the diphenolase activity of mushroom tyrosinase have been investigated. Theresults show that the alkylbenzoic acids assayed can lead to reversible inhibition of the enzyme; furthermore, o-toluic acid andm-toluic acid are mixed-type inhibitors and p-alkylbenzoic acids are uncompetitive inhibitors. The inhibition constants have beendetermined. For these p-alkylbenzoic acids, the inhibition strength follows the order: p-toluic acid < p-ethylbenzoic acid < p-propylbenzoicacid < p-isopropylbenzoic acid < p-tert-butylbenzoic acid < p-butylbenzoic acid < p-pentylbenzoic acid < p-hexylbenzoicacid < p-heptylbenzoic acid < p-octylbenzoic acid, indicating that the hydrophobic p-alkyl group played an important role in theinhibition of the enzyme. The inhibitory effects were potentiated with increasing lengths of the hydrocarbon chains. The inhibitoryeffects of o-toluic acid and p-isopropylbenzoic acid on the monophenolase activity have also been studied. The results show thatboth o-toluic acid and p-isopropylbenzoic acid can lengthen the lag time and decrease the steady-state activity of the enzyme.