Green tea has long been thought to possess anticancer properties. Additionally, the polyphenol components of green tea have demonstrated ability to inhibit 26S proteasome function. As there have been reports describing varied responses of gastric carcinoma cells to green tea treatment, the role of green tea treatment on proteasome function in the gastric carcinoma cell line AGS was investigated. Presented here are findings demonstrating that green tea extract is capable of inhibiting proteasome function of AGS cells. Furthermore, treatment of AGS cells with the green tea polyphenol (-)-Epigallocatechin-3-gallate resulted in a similar level of proteasome inhibition. It was also discovered in this study that proteasome inhibition in AGS cells resulted in a buildup of Kip1/p27 and IκBα, proteins that are involved in the progression through the G1/S checkpoint during cell division. Proteasome inhibition by (-)-Epigallocatechin- 3-gallate led to induction of apoptosis of AGS cells. Our results described here strongly suggest that green tea consumption is capable of inducing programmed cell death in gastric carcinoma cells through inhibition of proteasome activity. It should be noted, however, that consumption of green tea during anti-cancer protocols has been reported to reduce the effectiveness of a specific subset of chemotherapeutic compounds. In summary, consumption of green tea in gastric carcinoma patients may be effective in targeting cancer cells and slowing the progression of gastric cancers. Future studies of these natural products may provide some structural information which will allow for the development of the next generation of anti-cancer chemotherapeutics.