Abstract: Flavonoid was extracted from powder of mulberry leaves planted in Xinjiang with 60% (vol) ethanol aqueous solution under assistance of ultrasonic wave.Adopting enzymatic kinetic method,inhibitory action of the extract on tyrosinase activity was studied using L-dopa as the substrate.Results showed that the flavonoid extract displays rather strong inhibitory action on activity of tyrosinase.Its IC₅₀ was estimated as 0.2 g·L^-1.The inhibition mechanism was studied and it was found that the reaction is reversible and type of the inhibition belongs to the mixed type,with the inhibition equilibrium constants for inhibitor binding with free enzyme K_I and with enzyme-substrate complex K_IS were determined as 366 and 873 mg·L^-1 respectively.The DPPH (1,1-diphenyl-2-picrylhydrazyl) radical test results showed that the flavonoid extract has the antioxidant activity to a certain extent.The IC₅₀ is 25 mg·L^-1 that is similar to vitamin C.

Key words: whitening cosmetics additive, flavonoid from mulberry leaves, tyrosinase, inhibitory mechanism