Three flavonoids, luteolin (1), vitexicarpin (2) and artemetin (3), from the salt marsh plant Vitex rotundifolia, were tested for their anti-proliferative activities in AGS, MCF-7 and HT-29 human cancer cell lines and compared with the control using MTT assay. Among them, 2 was most effective with an IC50 of 6.9 and 22.8 microM against AGS and HT-29 cells, respectively. Inaddition, mRNA expression levels of major apoptosis-related genes such as p21, p53, Bcl-2 andBax in AGS cells were evaluated by reverse-transcription polymerase chain reaction (RT-PCR). Compound 2 not only enhanced most remarkably the expression level of tumor suppressor genes p53 and p21, and pro-apoptotic gene Bax at a concentration of 25 microM, but also suppressed the expression level of antiapoptotic gene Bcl-2 to 20% at the same concentration, thus shifting the Bax/Bcl-2 ratio in favor of apoptosis.