Objective To comparatively study anti-free radical and cytoprotective effects of quercetin(Q)and its monoglucoside isoquercetin(I),diglucoside rutin(R),which differs only in glycosyl-substitution at C-3 position of the molecules,using anoxia/hypoglycemia-induced cell injury model and thereby to explore the structure-effect relationship thereto.Methods The cell injury model was established by HEK293 cells cultured in vitro with Na2S2O3 plus sugar-free Earle’s fluid as incubation medium.Cell survival rate(CSR),total antioxidant capacity(TAC),SOD and LDH levels were determined.The effect intensity of the 3 flavonoids was compared by means of IC50,the concentration required to achieve 50% inhibition of the changes in the above indices in injured cells.Results Q,I and R all concentration-dependently elevated CSR,TAC and SOD and reduced LDH level.The all of IC50s for the above indices were ranked in order of IC50,QI >R.Conclusions The 3 structurally similar flavoloids all have significant and concentration-dependent anti-free radical and cyto-protective effects with the intensity being in order of aglycone>monoglucoside>diglucoside;the substitution of-OH by sugar group at C-3 position of flavoloids and increase in the sugar-substituent number are associated with the effect intensity reduced;namely,the intensity of these effects of flavonoids is negatively related the substutution by sugar group at C-3 position. Objective To comparatively study anti-free radical and cytoprotective effects of quercetin(Q) and its monoglucoside isoquercetin(I), diglucoside rutin(R), which differs only in glycosyl-substitution at C-3 position of the molecules, using anoxia/hypoglycemia -induced cell injury model and to to explore the structure-effect relationship. The Methods: The cell injury model was established by HEK293 cells cultured in vitro with Na2S2O3 plus sugar-free Earle’s fluid as incubation medium.Cell survival rate (CSR),total multiplet Capacity(TAC),SOD and LDH levels were determined.The effect intensity of the 3 flavonoids was compared by means of IC50,the concentration required to achieve 50% inhibition of the changes in the above indices in induced cells.Results Q,I and R all concentration-dependently elevated CSR, TAC and SOD and reduced LDH level. The all of IC50s for the above indices were ranked in order of IC50, Q I >R.Conclusions The 3 Structurally similar flavoloids all have significant and concentration-dependent anti-free radical and cyto-protective effects with the intensity being in order of aglycone>monoglucoside>diglucoside;the substitution of-OH by sugar group at C-3 position of flavoloids and increase in The sugar-substituent number are associated with the effect intensity reduced;namely,the intensity of these effects of flavonoids is negatively related the substutution by sugar group at C-3 position.