Abstract: Objective To observe the involvement of mitochondrial dysfunction in D-gal-in-duced aging model.Methods Respiratory chain activities (complex Ⅰ,Ⅱ,Ⅲ and Ⅳ)in brain mitochondria and ultrastructural impairments of hippocampal mitochondria were examined in the mice, which received 6 weeks D-galactose injection.Results Compared to the control group,D-galactose-injected mice showed decreased levels of brain mitochondrial respiratory chain and ultrastructural path-ological changes of hippocampal mitochondria.Conclusion Brain mitochondrial degeneration may be involved in D-galactose -induced brain aging.