Background: Survival of the semi-allograft fetus during pregnancy opens a new area for the immunological based causes of recurrent spontaneous abortion (RSA). Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) is a negative regulator of the T-cell activation, which may modulate peripheral self-tolerance of the allogeneic fetus. The present study aimed to investigate the +49 A/G CTLA4 genetic polymorphism and predisposition to RSA. Methods: The total participants were 120 women with at least two miscarriages and 120 healthy post-menopausal women as the control group. The +49 A/G polymorphism was genotyped using PCR-RFLP method. Required demographic information was collected through filling out a questionnaire. The obtained data were fed into SPSS software version 16. Results: The results showed a significant association between the minor alleles (G) with the decreased risk of the RSA. The frequency of the G allele in controls and patients was 25% and 12%, respectively. A GG genotype in the co-dominance model (OR: 0.25, 95%CI: 0.09-0.66) and in the dominant model for allele G (GG+AG vs. AA) (OR: 0.84, 95%CI: 0.8-0.87) showed significant association with RSA by imposing the protective role. The frequency of miscarriage is significantly (p=0.04) higher among the relatives of RSA women (33.3%) in comparison with the women in the control group (21.7%). Conclusion: It can be concluded that +49G allele may act as a dominant allele and reduce the risk of RSA. Family history of miscarriage increased the risk of RSA among women.