Abstract:In this paper，Agaricus bitorquis（Quél.）Sacc.was fermented by liquid fermentation ，and the intracellular and extracellular phenolic acid was extracted by ultrasonic-assisted method.The antioxidant activity of phenolic acids of A.bitorquis（Quél.）Sacc.during the fermentation was explored through the determination of mycelium biomass phenolic acid content，and the scavenging rate of intracellular and extracellular phenolic acids on 5 antioxidant indexes during fermentation.The results showed that the maximum mycelium biomass，intracellular phenolic acid content，and extracellular phenolic acid content were（22.91±0.21），（6.73±0.05）g/L and（10.11±0.05）g/L，respectively.The extracellular phenolic acid content was higher than the intracellular phenolic acid content.The intracellular and extracellular phenolic acids of A.bitorquis （Quél.）Sacc.had different scavenging abilities to different free radicals.The antioxidative activity was in a dynamic state during the fermentation，and the intracellular activity was higher than extracellular activity.The highest scavenging rate of intracellular phenolic acids to 2，2'-azinobis-（3-ethylbenzthiazoline-6-sulphonate）cation（ABTS+）radical，1，1-diphenyl-2-picrylhydrazyl（DPPH）radical，superoxide anion radical，and hydroxyl radical，and the iron ion reduction ability were 44.52%，50.54%，63.90%，29.35% and 7.17%，respectively.The highest scavenging rate and the iron ion reduction ability of extracellular phenolic acids were 47.32%，34.39%，23.95%，28.61% and 3.67%，respectively.Therefore，intracellular and extracellular phenolic acids of A.bitorquis（Quél.）Sacc.are good sources of natural antioxidants.