Lobeliae chinensis Herba ("ban bian lian"), Rheum officinale Baill. ("da huang"), Sanguisorba officinalis Linn. ("di yu"), Agrimonia pilosa Ledeb. ("xian he cao"), and Paris polyphylla Smith ("zhi hua tou") are well-known traditional Chinese medicines. They are commonly used in traditional Chinese medicine formulae against cancer. In this study, the antioxidant and anticancer effects of water extracts of these herbs were investigated. In the antioxidant and anticancer studies, water extracts of di yu, xian he cao, and da huang were show to be the most antioxidative and had the highest growth inhibitory effect on human lung adenocarcinoma A549 cell and human breast cancer MCF-7 cell. By comparing their percentage free radical scavenging capacity (SR%) and percentage growth inhibition on A549 and MCF-7 cells, a positive linear relationship between antioxidant activity and anticancer effect of the five herbal water extracts was found. This suggested that the antioxidants of the herbal water extracts might contribute to their anticancer effects on A549 and MCF-7 cells. ; Department of Applied Biology and Chemical Technology