Tyrosinase is key enzyme for the biosynthesis of melanocyte. In order to explore the effects of flavonoid on the activity of tyrosinase, we extracted flavonoid from bamboo shells by ethanol ultrasonication and purified it by AB-8 macroporous resin. The inhibitory effects of bamboo shell flavonoid extract on the monophenolase and diphenolase activities of tyrosinase were studied by an enzyme kinetic method. The concentration of bamboo shell flavonoid extract which caused the enzymatic activity loss of 50% was 5.6 mg/mL for monophenolase and 4.6 mg/mL for diphenolase. Bamboo shell flavonoid extract of 8.0 mg/mL extended the time of delay in monophenolase from 1.4 to 4.2 min. An analysis of inhibition kinetics suggested that bamboo shell flavonoid extract was a reversible mixed inhibitor for the oxidation of L-DOPA, and the inhibition equilibrium constants for inhibitor binding with free enzyme Ki and with enzyme-substrate complex Kis were 3.1 mmol/L and 5.7 mmol/L, respectively. The results indicate that the bamboo shell flavonoid extract can inhibit the monophenolase and diphenolase activities of tyrosinase.