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The authors describe a rapid and sensitive method for the determination of the activity of scavenging hydrogen peroxide in which glucose oxidase-stabilized gold nanoclusters (AuNCs) were employed as a fluorescent nanoprobe. The AuNCs are synthesized by a biomineralization process and display an intense blue fluorescence peaking at 450 nm and a quantum yield of 1.1% under 360-nm excitation. The Fenton reaction induces quenching of fluorescence, and this effect can be used to determine H 2 O 2 in the 0.5 to 10 μmol⋅L −1 concentration range. The substances displaying H 2 O 2 scavenging activity prevent quenching and thus restore fluorescence. The intensity of restored fluorescence is directly related to the H 2 O 2 scavenging activity of the antioxidant. The method was applied to the determination of the H 2 O 2 scavenging activity of the model antioxidants ascorbic acid and tartaric acid which gave IC 50 values of 7.4 and 19.1 μmol⋅L −1 , respectively.