Beta 3-adrenergic receptors are expressed mainly in adipose tissues and play an important role in lipolysis and thermogenesis. Chronic administration of beta 3-adrenergic receptor agonists into obese rodents reduce the size of adipocytes by the breakdown of triglyceride and ameliorate insulin resistance associated with the normalization of the expression of adipocytokines, such as leptin and tumor necrosis factor-alpha. However, acute administration of the drugs induce remarkable insulin secretion, the mechanism of which is still unclear. Although the effect of beta 3-adrenergic receptor agonists may be different between rodents and human, these drugs are promising as anti-obese or anti-diabetic agents, and several clinical studies are underway.