Objective To study the antiviral effect and the best decoction time of Yinqiao Powder（ 银翘散）.Methods Seventy-two mice were randomized into Yinqiao Powder 3-minute group

6-minute group and 12-minute group

blank control group

model control group and positive control group

with 12 mice in each group. Besides the blank control group

mice in other groups were infected by nasal dripping with 15 LD50 of influenza A virus mouse lung adaptive strain FM1

0. 05 ml on each mouse. Groups of Yinqiao Powder at different decoction time（ 3

6

12minutes） were given corresponding Yinqiao Powder decoction by gavage

0. 5 ml each time

once every day from the infected day for 7 days. The positive control group was given 27. 5 mg /（ kg·d） of oseltamivir phosphate capsules by gavage. The blank control group and the model control group were given 0. 2 ml /10 g of distilled water by gavage. The lung index

lung index inhibition rate and the spleen index of mice in each group were compared on the 3rd and the7 th day. Relative virus load in mice lung tissue were detected. Results Compared with those in the blank control group

the lung index and virus load in the model control group increased significantly on the 3rd and 7th day（ P <0. 05）. Compared with those in the model control group

the lung index decreased on the 3rd day in the positive group

the Yinqiao Powder 3-minute group and Yinqiao Powder 6-minute group; the lung index and lung tissue virus load decreased significantly on the 7th day in the positive group and all Yinqiao Powder groups（ P < 0. 05）. There was no significant difference in spleen index of mice in all groups between the 3rd day and the 7th day（ P > 0. 05）.On the 3rd day and the 7th day

the virus inhibition rate in the Yinqiao Powder 3-minute group was most closed to that in the positive group. Conclusion Yinqiao Powder seems to have antiviral effect on influenza A virus mouse lung adaptive strain FM1 infected mice. The best decoction time is 3 to 6 minutes.