Background: Recurrent pregnancy loss (RPL) is defined as two or more miscarriages before the 20th week of gestation and its etiology is unknown in 50% of the cases. Interleukin 6 is an immune mediator, plays a regulatory role in embryo implantation and placental development. Objective: The purpose was to assess the association between IL-6 -634C/G polymorphism and, susceptibility to idiopathic RPL for the first time in Iran. Materials and Methods: In total 121 women with RPL and 121 healthy women as control group were enrolled in this case-control study. This study was performed from August 2013 to October 2014 in the Molecular Genetics Laboratory of Arsanjan University. Candidate polymorphism was evaluated by PCR-RFLP method on extracted genomic DNA. Data was analyzed using the statistical SPSS package. Results: Our results showed an increased risk of RPL in patients with GG + GC genotype (OR=5.1, 95%CI: 1.04-25.3, p=0.04) in comparison to CC genotype. The frequency of mutant allele G in patients and controls was 0.75 and 0.66 respectively. The mutant allele G predisposes women to miscarriage 1.5 times greater than controls (OR=1.5, 95%CI: 1.03-2.27, p=0.036). The mean number of live births in RPL women (1.3±2.3) was significantly lower compared to control women (4.8±2.3). Conclusion: This study indicated that the promoter polymorphism (-634C/G) of the IL-6 gene has likely influence on individual susceptibility to RPL.