Several treatments for skin pigmentation are available today, however, many have unwanted side effects. Classic drugs like hydroquinone, arbutin, mequinol and kojic acid have been considered strongly carcinogenic, with related adverse effects. Traditional Chinese medicines (TCMs) have long been documented for their skin-lightening properties with little known negative effects. However, little is known about precisely how these herbal medicines work and what are the chemical basis for their activity. In this project, a 96-well plate based tyrosinase assay was established and used to test 44 TCM with known skin-lightening properties. Out of 44, 17 TCM extracts showed over 60% inhibition against tyrosinase at the concentration of 0.5 mg/mL. One of the TCM extracts, Xanthium strumarium L. extract, possessed 81.7% inhibition at 0.5 mg/mL. Further bioassay-guided isolation of the crude extract resulted in 10 compounds. Three of the compounds showed moderate activity against tyrosinase with IC50 values of 0.18 mM (cytidine), 0.29 mM (1,4-dicaffeoylquinic acid) and 2.47 mM (xanthiside). Chapter 1 contained the introduction of this project as well as the literature review. Chapter 2 was mainly about the screening of TCM extracts against mushroom tyrosinase. Chapter 3 contained the bioassay-guided extraction and isolation of Xanthium strumarium L. Additionally, the IC50 values of the active compounds were included in chapter 3 as well.