〔Abstract〕 Abstract Objective To investigate the association between single nucleotide polymorphism ( SNP) of PROS1 gene and recurrent spontaneous abortion (RSA) in Baotou Han population . Methods 158 RSA patients and 158 control subjects were selected as the study subjects , and the activities of protein S , protein C and antithrombin-Ⅲ were measured . The rs13062355 , rs6441600 and rs12634349 loci of PROS1 gene were genotyped by polymerase chain reaction-restriction fragment length polymorphism ( PCR-RFLP) . Non-conditional Logistic regression was used to analyze the correlation between three SNPs of PROS1 gene and the risk of RSA . Results The protein S and antithrombin-Ⅲ activities of RSA patients decreased significantly ( P < 0. 05) . PROS1 SNP rs13062355 was associated with the risk of RSA under the dominant model : compared with genotype TT , patients with CT + CC gen- otypes had a reduced risk of RSA (OR = 0. 398 , 95% CI: 0. 249 - 0. 638) ; SNP rs6441600 and rs12634349 were not associated with the risk of RSA (P > 0. 05) . In the haplotypes constructed by PROS1 rs13062355 , rs6441600 and rs12634349 , Haplotype C-C-C was statistically different between the two groups( P < 0. 05) . The third-order interaction model rs13062355-rs6441600-rs12634349 was associated with the risk of RSA . Conclusion PROS1 SNP rs13062355 may be associated with the risk of RSA in Han women in Baotou area. Haplotype C-C-C of PROS1 rs13062355 , rs6441600 and rs12634349 reduces the risk of RSA . The third-order model rs13062355-rs6441600 - rs12634349 interaction has a synergistic effect on the occurrence of RSA .