Objective:To observe the effects of modified Wuzi Yanzong Granule(加味五子洐宗颗粒,WYG)on memory function and the activity of serum superoxide dismutase(SOD),malondialdehyde(MDA)levels,leukocyte mitochondrial DNA(mtDNA)deletion rate and β-amyloid protein1-28(Aβ1-28 )in patients with mild cognitive impairment(MCI).Methods:Thirty-six patients with MCI were selected based on the internationally recognized Petersens criteria,and equally and randomly assigned to two groups.The treated group was treated with WYG and the control group was treated with placebo for 3 months.In addition,20 healthy subjects were included in the study as the normal control group.Changes of memory function,SOD activity,MDA content,leukocyte mtDNA deletion rate and Aβ1-28 content were observed before and after treatment.Results:Compared with the normal control group,the memory quotient and SOD activity in patients with MCI decreased significantly(P＜0.01),while MDA,Aβ1-28 levels and the leukocyte mtDNA deletion rate increased significantly(P＜0.01).After treatment,levels of memory quotient and serum SOD activity increased while the serum MDA level,leukocyte mtDNA deletion rate and Aβ1-28 level decreased in the treated group compared with those before treatment(P＜0.01,P＜0.05).Meanwhile,leukocyte mtDNA deletion rate and Aβ1-28 content in the treated group were all lower than those in the control group(P＜0.05).Conclusion:WYG could improve memory function in patients with MCI and the therapeutic mechanism is possibly related to the increased activity of anti-oxidase,the improved free radical metabolism and the alleviation of leukocyte mtDNA oxidation damage.WYG shows clinical significance in delaying the progression of MCI.