Abstract: T helper 17 （Th17）cells were recently found to bea subgroup of independent T cells, whichare distinct from Th1 and Th2 cells. Th17 may play an important role in the inflammation development related topathogenetic mechanism of autoimmune diseases and acute transplant rejection. Now，the new Th1/Th2/Th17 and Treg balance model has replaced the Th1/Th2 paradigm，which is considered to play an essential role in maintaining the immune tolerance during pregnancy. As a common disease in clinical，the immunological pathogenesis of unexplained recurrent spontaneous abortions （URSA）is still unknown. Th17 cells could provide us a new research target on the pathogenesis and treatment of URSA.

Key words: T-lymphocytes, regulatory, Immune tolerance, Pregn, Abortion, habitual, Interleukins