Quercetin and other polyphenols have anti-carcinogenic and anti-tumorigenic activity in various organs, however, studies of this activity are lacking in endometrial cancer. We hypothesize that quercetin has anti-proliferative activity and the mechanisms of quercetin action may be through modulation of cell cycle and cell growth regulatory genes. To test this hypothesis, we treated endometrial cancer cells (Ishikawa cell line) with quercetin, and cell proliferation, expression of growth signal genes (EGF, VEGF, and TGF-alpha), cell cycle genes (p53, p21, p73, and cyclin D1), and apoptosis-related genes (bcl-2 and bax) were analyzed. Results of these experiments demonstrate that after a 7-day exposure to 1, 10 and 100 micro M of quercetin, growth of Ishikawa cells was inhibited by 3, 51 and 87%, respectively. The gene and protein expression data suggest that quercetin treatment (100 micro M) significantly decreased EGF and cyclin D1, whereas VEGF was up-regulated in Ishiwaka cell lines. Other genes such as TGF-alpha, p53, p21, p73, bcl-2 and bax were not significantly changed with quercetin treatment in Ishiwaka cell lines. The present study suggests that quercetin can suppress proliferation of Ishikawa cells through down-regulation of EGF and cyclin D1.