Abstract: This research was performed to study the effect of date palm fruit (Phoenix dactylifera L.) on the hepatic enzyme system glutathione-S-transferase (GST) in rats with 7, 12-dimethylbenz (alpha) anthracene (DMBA)-induced mammary cancer. The effect of feeding the fruit was compared to that of feeding raw soybean seeds and injection with 2 drugs (preventive and curative against mammary cancer) i.e., tamoxifien and 17-beta-estradiol. Eighty three female weanling Sprague-Dawley rats were randomly distributed into 8 groups. Each group received one of the dietary or drug treatments. One of the groups was injected with sesame oil which is the carcinogen vehicle, to serve as a negative/DMBA control group. Another group of rats that received neither drug nor special dietary treatment served as a positive/DMBA control group. The experiment lasted for 26 weeks. At the end of the feeding period, all animals were killed, livers were removed, prepared and analyzed for their protein content and GST enzyme activity. Livers of the rats that were injected with sesame oil vehicle showed the highest enzyme activity. The rats which were fed the date palm fruit tended to (p = 0.079) reduce the enzyme activity. It is concluded that the date palm fruit at the 2 maturity stages may possess antioxidant activity that is reflected positively in the prevention of DMBA-induced mammary cancer.