The article presented literature review about of endogenous opioid system (EOS) formation consist of opioid receptors complex and its ligands (endogenous opioid peptides) in different tissues including placenta. It was shown that formation of fetal EOS is going with anatomic and functional development of the central nervous system and EOS expression begins in the placental tissues as soon as implantation and starts till the end of the pregnancy. Influence of opioid peptides on secretion progesterone, prolactin family peptides, growth hormone, placental lactogens and prolypherine from the trophoblast tissue is discussed.