Abstract: The mulberry jiaosu is a fermentation product which is made from mulberry juice adding probiotics for fermentation.The changes of mulberry jiaosu'physiological activity in its fermentation process was studied. The changes of the content of glucose, fructose, ethanol, organic acids, anthocyanins, procyanidins and the total phenol were determined by HPLC and colorimetric methods.To explore the effect of fermentation on the antioxidant activity of mulberry jiaosu by hydroxyl radical scavenging experiments and DPPH· scavenging experiments.The results indicated that the total content of glucose and fructose decreased to 66.58 mg/m L after 30 days fermentation, but the ethanol, lactic acid and acetic acid content was greatly improved to 27.19, 4.03 and 4.69 mg/m L respectively in the end.The results of the active constituent experiment showed that the content of anthocyanins and procyanidinsc reduced, but the total phenol content increased by 5.0% and the antioxidant activity was also enhanced after 30 days of fermentation. The scavenging rate of hydroxyl radicals and DPPH· were 48.12% and 98.16%, respectively.Therefore, the antioxidant activity of mulberry jiaosu has been improved in the fermentation process and its change was relevant to the change of total phenolics.