AIM:Antioxidants act mainly through two routes:induction of antioxidant enzymes(enzymatic)or direct reaction with reactive oxygen species(ROS)(non-enzymatic),but the one taken by the extract of Ginkgo biloba(EGb)remains to be investigated.In present study,EGb was tested for both of the antioxidant routes in vitro.METHODS:The induction of EGb on two antioxidant enzymes,glutamate cysteine ligase catalytic subunit (GCLC)and glutathione-S-transferage subunit-P1(GST-P1),in cell lines wag detected by Western-blot.The effects of EGb on superoxide anion radical(O2·-),hydroxyl radical(OH·),rat erythrocyte hemolysis and lipid peroxidation of rat liver homogenate were determined by activity methods respectively.RESULTS:EGb was dem onstrated significantly to induce the two antioxidant enzymes(GCLC and GST-P1),directly scavenge superoxide anion radical(O2·-),hydroxyl radical(OH·)and inhibit rat erythroeyte hemolysis and lipid peroxidation of rat liver homogenate.CONCLUSION:The results strongly support the notion that EGb plays dual antioxidant roles: induction of antioxidant enzymes and direct reaction with ROS.