We investigated whether three flavonoids including daidzein, baicalein, hesperidin and ursolic acid, a triterpene acid, affect proliferation of MCF-7 human breast cancer cells stimulated by estrogenic compounds. Ursolic acid and baicalein inhibited proliferation of MCF-7 cells induced by PhIP, a food-derived carcinogen with estrogenic activity. Daidzein and hesperidin inhibited estradiol-induced proliferation of MCF-7 cells. These compounds should be further investigated for the possible involvement in signaling pathway after estrogen receptor binding in breast cancer cells.