Flos Sophora was used as a raw material for solid-state fermentation by Aspergillus niger M8, and changes of quercetin contens in Flos Sophora before and after being fermented were tested by HPLC. The results showed that after solid-state fermentation of Flos Sophora by Aspergillus niger M8, most of the rutin -95 62%- was transformed to quercetin and the quercetin content was increased from 3 28 mg/g to 39 23 mg/g, which was 11 96 times higher than unfermented Flos Sophora . The serum uric acid -SUA- content of mice treated by different doses -400 mg/kg and 200 mg/kg- of fermented Flos Sophora was decreased 24 37% and 17 96%, which was significantly - P <0 01- lower than that in the model group. However, the SUA content of mice treated by the high does of unfermented Flos Sophora -400 mg/kg- was only 2 23% lower than that of the control group. The results demonstrated that the solid-state fermentation by Aspergillus niger M8 could improve the reducing-SUA activity of Flos Sophora . Moreover, the blood urea nitrogen -BUN- and serum creatinine -SCr- contents in fermented Flos Sophora treatment groups were significantly - P <0 05- lower than these in the model group, which indicated that fermented Flos Sophora could reduce the injury of drugs on mice kidneys. In addition, the safety of the product was tested by the acute toxicological experiment