Active oxygen species alter the activities of the enzymes involved in the defence against free radicals and substantially influence the aging process and age-dependent neuropathology. Unilamellar liposomes were used to deliver flavonoidal antioxidant quercetin (QC) to rat brain. Antioxidant potential of QC loaded in mannosylated (QC 7.2 micromol/kg b.wt.) liposomes (50 nm) was investigated by an in vivo model of cerebral ischemia and reperfusion on Sprague Dawley young (2 months old, b.wt. 160-180 g) and aged (20 months old, b.wt. 415-440 g) rats. Animals were made ischemic for 30 min by bilateral clamping of the common carotid artery followed by a 30 min cerebral reperfusion by withdrawing the clamping. Diene level and (GSSG/GSH) ratio were found to be higher in normal aged, compared to normal young rat brain. Superoxide dismutase, catalase, glucose-6-phosphate dehydrogenase, glutathione reductase and glutathione S-transferase activities were lower in normal aged rat brain. Further reduction of these antioxidant enzymes was observed in aged rat brain by the induction of cerebral ischemia and reperfusion. Mannosylated liposomally encapsulated QC treatment resulted in a significant preservation of the activities of antioxidant enzymes and a marked inhibition of cellular edema formation in neuronal cells of young and old rats.