Mitochondria have long been recognized as ATP engines for the cell and recently as a dynamic and mobile organelles that control cell death and life. This exquisite organelle is the site of reactive oxygen species production and is highly vulnerable to exogenous stresses, resulting in catastrophic damage to the cell. Mitochondrial dysfunction is linked to a wide range of age-associated degenerative diseases, such as metabolic syndrome, cardiovascular disease, and neurodegenerative diseases. Understanding the molecular mechanisms of mitochondria-dependent pathogenesis may provide important strategies to treat these diseases. Indeed, mitochondria are emerging therapeutic targets for the mitochondria-related diseases. In this paper, we review the recent concepts of mitochondrial biology and how mitochondria are involved in age-associated degenerative diseases. Furthermore, we summarize the therapeutics which target to improve mitochondrial functions.