Increasing energy expenditure through activation of brown adipose tissue (BAT) is a critical approach to treating obesity and diabetes. In this study, rutin, a natural compound extracted frommulberry and a drug used as a capillary stabilizer clinically formany yearswithout any side effects, regulated whole-body energymetabolism by enhancing BAT activity. Rutin treatment significantly reduced adiposity, increased energy expenditure, and improved glucose homeostasis in both genetically obese (Db/Db) and diet-induced obesity (DIO) mice. Rutin also induced brown-like adipocyte (beige) formation in subcutaneous adipose tissue in both obesity mouse models. Mechanistically, we found that rutin directly bound to and stabilized SIRT1, leading to hypoacetylation of peroxisome proliferator-activated receptor g coactivator-1a protein, which stimulated Tfam transactivation and eventually augmented the number of mitochondria and UCP1 activity in BAT. These findings reveal that rutin is a novel small molecule that activates BAT and may provide a novel therapeutic approach to the treatment of metabolic disorders.-Yuan, X.,Wei, G., You, Y.,Huang, Y., Lee,H. J.,Dong,M., Lin, J.,Hu, T., Zhang,H.,Zhang,C.,Zhou,H., Ye, R., Qi, X., Zhai, B., Huang, W., Liu, S., Xie, W., Liu, Q., Liu, X., Cui, C., Li, D., Zhan, J., Cheng, J., Yuan, Z., Jin, W. Rutin ameliorates obesity through brown fat activation. FASEB J. 31, 333-345 (2017). www.fasebj.org.