Abstract: In order to investigate underling mechanism for the antioxidant activity of Liuyang Douchi,the contents of antioxidants(including polyphenols,flavonoids and soybean isoflavones)and the antioxidant activity of Liuyang Douchi during fermentation were measured. Results showed that although the content of total flavonoids of Douchi decreased gradually,the glycoside type soybean isoflavones accounted for 85.75% at the beginning of fermentation while aglyn-type soybean isoflavones accounted for 81.41% at the end of the fermentation. The total polyphenols increased from 2.78 mg/g to 5.76 mg/g by fermentation,and the total antioxidant capacity,DPPH·,hydroxide(·OH),superoxide anion(O₂^-·)radical-scavenging rate of Douchi increased to 1088.91 U/g,93.67%,90.23%,88.38%,respectively.In addition,the results of correlation analysis showed that aglycogenic soybean had a greater effect on the antioxidant activity of Douchi than total polyphenols.It indicated that fermentation was helpful to the increase of total polyphenols in soybean and the conversion of glycosidic soybean isoflavones to aglycone isoflavones,which was one of the key factors to enhance the antioxidant capacity and improve the functionality of Liuyang Douchi.