Effect of acute exposure of male rats to estradiol valerate once a week for 3 weeks on the activity of phase I, phase II and lysosomal glycosidases has been studied. Treatment caused a significant reduction in both body and liver weight, however, the liver/body weight ratio was not changed. Phase I monooxygenases enzymes activities showed a significant decrease in the hydroxylation of benzo (a) pyrene, demethylation of methoxycoumarin, and deethylation of ethoxyresorufin. Phase II showed a significant increase in the glucuronidation of phenolphthalein, and a decrease in the glucuronidation of 4-methylumbellierone and p-nitrophenol.Also, estradiol treatment caused a significant elevation in the hepatic glycosidases activity.