Abstract: Testicular Leydig cells are main tissular cells which produce and secret androgen. The fetal Leydig cells are differentiated from the interstitial precursor cells, and postnatal Leydig cells from mesenchymal stem cells. Adolescent Leydig cells are differentiated and proliferated from the pleuripotent interstitial precursor cells, at three discontinuous developmental stages of precursor Leydig cells, immature Leydig cells and mature Leydig cells. Differentiation and development of Leydig cells in fetal stage and postnatal stage are regulated by many factors. Developmental regulators of fetal Leydig cells include the sexual determination gene Y, neurocyte adhesion molecules, transforming growth factor（TGF） and anti-Müllerian hormorne（AMH）. Proliferation and maturation, as well as differentiation, of Leydig cells after birth are regulated by endocrine, autocrine and paracrine mechanisms, such as luteinizing hormone（LH）, intratesticular androgen, estrogen, insulin-like growth factor 1（IGF-1）, calretinin and many other local cytokines.

Key words: Leydig cells, Androgens, Mesenchymal stem cells, Cell proliferation