The silent information regulator protein 2 (Sir2) and its homologues play an important role in the regulation of cellular physiological processes such as survival, apoptosis, and aging. SIRT1, the mammalian Sir 2 homologue, has been shown to deacetylate a wide range of non-histone substrates and histone substrates. It has been constantly reported that SIRT1 may be associated with the occurrence of metabolic syndrome, genomic homeostasis, tumors, and neurodegenerative diseases. Calorie restriction may mitigate many major diseases in rodent models by SIRT1-mediated deacetylase activity and prolong the life expectancies in these animals. Therefore, SIRT1 may be emphasized as a new therapy target for many different diseases.