The effect of date palm fruit feeding (to female Sprague-Dawley rats with 7,12-dimethylbenz(a)anthracene–induced mammary cancer) on the hormone 17-ß-estradiol concentration was compared to that of feeding soybean seeds and injection with two drugs (one preventive against and the other curative for 7,12-dimethylbenz(a)anthracene-induced mammary cancer i,e. tamoxifen and the hormone 17-ß-estradiol). The date palm fruit raised the hormone concentration significantly (p < 0.05). The hormone concentration was positively correlated with the palpable tumor latency, and negatively correlated with tumor incidence rate and multiplicity. It is concluded that the preventive effect of the date palm fruit against 7,12-dimethylbenz(a)anthracene-induced mammary cancer is related to the effect on the hormone 17-ß-estradiol.