We have previously reported the changes of mitochondrial function and/or antioxidative enzyme efficiency in a few organs of rats as a result of aging. However, there is a further need to reach a conclusion about their interactions in biological functions based on other evaluation tips like the usage of advanced methods and the exploring of crucial biochemical parameters. Therefore, we investigated the mitochondrial inner membrane functional integrity by the analysis of respiration control ratio and membrane potential in the liver and brain of young (8 months) and old (26 months) Fischer 344 rats. The disintegration of mitochondrial membrane integrity was determined higher in the liver of old rats than that of young rats. This was well correlated with the decrease of total superoxide dismutase (SOD), Cu/Zn-SOD, Mn-SOD and glutathione peroxidase activities in most of the organs, except for the increase of catalase activity in heart of old rats. Similarly, the protein expressions of these enzymes were down regulated in the liver and kidney of old rats. Taken together, we suggest that the mitochondrial malfunction in old rats is associated with the decrease of antioxidative enzyme efficiency. And the data are also discussed with changes in the results from inter-laboratories.