Abstract: Saffron was used as the redox reaction indicatorin the rapid determination of the antioxidant activity of the fermentation broth of Agrocybe chaxinguHuang. Fenton reaction was modified for the methodology development by comparing the effect of safranin usage, sample volume, pH, and vitamin C on the light absorbance measured on a spectrophotometer. The optimized conditions included pH 7.0-7.5 with an increased volume on the 520 μg·mL^-1safranin solution from 0.5 mL to 2.0 mL anda much-reduced usage on the sample solution from 7.0 mL to 0.5 mL. The absorbance reading remained constant within 30 min. Under the conditions, vitamin C was applied as a standard hydroxyl radical scavenger to evaluate the antioxidant activity of A. chaxingu broth. The results showed that the hydroxyl radical-scavenging ability of the A. chaxingu intracellular metabolites was 48.62%-65.43% (equivalent to vitamin C 72.62-90.22 mmol·L^-1), and that of the extracellular metabolites, 57.59%-72.82% (equivalent to vitamin C 82.02-97.96 mmol·L^-1). The newly established rapid determination method was, thus, confirmed for its validity. In addition, there were no toxic reagentsapplied in the testing that would cause any safety concerns.