Estrogens are considered the major breast cancer risk factor, and the carcinogenic potential of estrogens might be attributed to DNA modification caused by derivatives formed during metabolism. $17{eta}$-estradiol ($E_2$), the main steroidal estrogen present in women, is metabolized via two major pathways: formation of 2-hydroxyestradiol (2-OH $E_2$) and 4-hydroxyestradiol ($4-OH;E_2$) through the action of cytochrome P450 (CYP) 1A1 and 1B1, respectively. Previous reports suggested that $2-OH;E_2$ has putative protective effects, while $4-OH;E_2$ is genotoxic and has potent carcinogenic activity. Thus, the ratio of $2-OH;E_2/4-OH;E_2$ is a critical determinant of the toxicity of $E_2$ in mammary cells. In the present study, we investigated the effects of berberine on the expression profile of the estrogen metabolizing enzymes CYP1A1 and CYP1B1 in breast cancer MCF-7 cells. Berberine treatment produced significant induction of both forms at the level of mRNA expression, but with increased doses produced 16~ to 52~fold greater induction of CYP1A1 mRNA over CYP1B1 mRNA. Furthermore, berberine dramatically increased CYP1A1 protein levels but did not influence CYP1B1 protein levels in MCF-7 cells. In conclusion, we present the first report to show that berberine may provide protection against breast cancer by altering the ratio of CYP1A1/CYP1B1, could redirect $E_2$ metabolism in a more protective pathway in breast cancer MCF-7 cells.