The ob factor, Leptin, produced from white adipose tissue is classified as a “metabolism modifier" or lipostat" or “adipostat" and it have myriad effects on tissues and endocrine systems that ultimately lead to the coordination of whole-body energy metabolism. Leptin seem to be involved in pregnancy, puberty, immune modulation, inflammation, wound healing and mutation. In coordination with mammary milk leptin, plasma leptin may act as an autocrine or paracrine signaling molecule on the mammary gland epithelial cell proliferation, differentiation, growth, apoptosis and function during early lactation period; by repartitioning of plasma nutrients towards milk secretion. It seems that the basal level of plasma leptin might be important for mammary gland to function normally and it might be involved in thermoregulation, satiation, endocrine homeostasis and systemic regulation in the neonate.