An electrochemical biosensor for assessment of the antioxidant activity of antioxidants was fabricated by immobilizing guanine,poly(dimethyldiallylammonium chloride) (PDDA),Fe@Fe2O3 core–shell nanonecklace and glucose oxidase (GOX) in sequence on an activated glassy carbon electrode (GCE).The glucose oxidase (GOX) was kept good bioactivity in the composite membrane.In glucose solution,the hydroxyl radical (·OH) was generated in the membrane via a series of reactions and damaged guanine in situ.As adding antioxidants ascorbic acid,caffeic acid,coumaric acid and resveratrol into the damage system,these antioxidants could alleviate the guanine damage degree.By recording the square wave voltammetric signal change of the guanine,the antioxidant capacities of the four antioxidants were evaluated.The sensor exhibited good reproducibility and stability for rapid assessment of the antioxidant capacity.