The measurement system for in vitro screening whitening agents was constructed according to the kinetic studies of home-made potato tyrosinase with catechol as substrate.And the tyrosinase inhibitory activity of 12 Traditional Chinese Medicines was measured.The optimum reaction temperature and pH of potato tyrosinase were 30 ℃ and 6.5 respectively.The maximum absorbance wavelength of the enzymatic-induced product was 420 nm when using cateehol as substrate.