context: portal hypertension is a complication secondary to cirrhosis that is characterized by increased blood flow and/or vascular resistance in the portal system, causing the appearance of a hyperdynamic collateral circulation. partial portal vein ligation is an experimental model used in rats to study the pathophysiological mechanisms involved in pre-hepatic portal hypertension. estrogen e2 is an antioxidant molecule with various physiological actions. objectives: to evaluate the antioxidant activity of endogenous estrogen in an experimental model of partial portal vein ligation by comparing intact with castrated rats. methods: twenty wistar rats, weighing on average 250 g were used and divided into four groups: sham-operated (so); intact (i) with partial portal vein ligation (i + ppvl), castrated (c) and castrated with partial ligation of the vein (c + ppvl). day 1: castration or sham-operation; day 7, ppvl surgery; on day 15 post-ppvl, portal pressure in the mesenteric vein of rats was measured on polygraph letica. lipid peroxidation in the stomach was assessed using the technique of thiobarbituric acid reactive substances and activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase. statistical analysis was done with anova - student-newman-keuls (mean ± se), and p<0.05 was considered as significant. results: portal pressure was significantly increased in c + ppvl as compared to the other groups. there was no significant difference in the group of intact rats. tbars showed significant damage in c and c + ppvl in relation to others. antioxidant enzymes were significantly increased in the castrated rats with subsequent ppvl as compared to the other groups. conclusion: we suggest that estrogen e2 plays a protective role in intact compared with castrated rats because it presents hydrophenolic radicals in its molecule, thus acting as an antioxidant in this experimental model.