Objective To determine the concentrations of progesterone-induced blocking factor and T helper-1 type(Th1)/T helper-2 type(Th2) cytokine in serum of patient with recurrent spontaneous abortion(RSA)and to study their clinical significance．Methods The PIBF、IL-2、TNF-α、IFN-γand IL-10 concentrations in serum of 94 RSA patients were measured by enzyme-linked immunosorbent assay(ELISA)．72 nonpregnant woman and 92 normal pregnant women were controls .Results IL-2、TNF-α、IFN-γ concentrations in serum of RSA were significantly higher than those in normal pregnant women (P<0．05)，while PIBF、IL-10 concentrations in RSA group were lower than those in normal pregnant women (P<0．05)．Conclusion The changes obviously decrease of expression of PIBF in serum of RSA group maybe one of the important cause of RSA．Thl/Th2 balance was related to RSA， it maybe one of the important routines transferring RSA．PIBF plays an important role in regulating the balance of Thl/Th2 cytokines