Objective:To explore the free radical mechanism of Zuoguiyin(ZGY) in delaying senility.Methods:After the ZGY group of mice had freely drunk the concentrated decoction for 75 days

and compared with the old control group

we observed the effect on the indices of thymus index

spleen index

the contents of MDA

the activities of SOD and T-AOC of serum.Results:Compared to the young control group

the old control group showed significant increase in the contents of MDA in blood

significant decrease in the activities of SOD

T-AOC in blood

and decrease in thymus index and spleen index.The ZGY group showed significant improvement for the above parameters compared with the old control group.The differences were statistically significant.Conclusion:Zuoguiyin could delay the senility

which might be related with increasing antioxdation and thymus index and spleen index

meanwhile

reducing the damage of free radical to cell membrane.