Anticancer activity screening of an extract library containing 152 traditional Chinese medicines (TCM) has identified one crude extract from Taxodium ascendens with potent activity. The overall aim of the project was to investigate the chemical composition of the TCM extract and to evaluate the activities of the natural products against cancer cell lines. In Chapter1, it introduces the background of traditional medicines & natural products and also exemplifies several nature-derived-drugs. A review based on anticancer drugs derived from natural products and the importance of natural origin compounds against cancer were also discussed. A high throughput screening assay for 152 TCMs suggested the potential anti-breast cancer activities of MeOH and EtoAc extracts of Taxodium ascendens. Therefore, it was selected for large scale chemical investigation. Chapter 2 details the large scale isolation and structure elucidation of pure natural products from Taxodium ascendens extract. A total of 15 compounds were isolated from 6.25 grams of crude extract. They represented four structural classes including diterpenes, flavonoids, terpene acids and aromatic acids. The structures of the compounds were elucidated via 1D- and 2D-NMR and Mass spectroscopic data. Cytotoxic assays of three compounds were tested against a breast cancer cell line, T-47D. One compound, 6-hydroxy-5,6-dehydrosugiol (2.23), showed potent activity against T-47D with an IC50 value of 8.24 M. The physical chemical properties of all the isolated compounds were also evaluated against Lipinski’s rule of five. The detailed experimental procedures can be found in Chapter 3. In conclusion, 15 pure natural products were isolated with 6-hydroxy-5,6-dehydrosugiol (2.23) showing potent anticancer activity.