SYCP3 (Sinaptonemal complex protein 3) plays a critical role in pairing and recombination of homologous chromosomes in meiosis 1. It has been shown that lack of this gene leads to infertility in male and weakened fertility in female mice. In a case-control study, we investigated the SYCP3T657C polymorphism in the genome of 100 Iranian women with recurrent pregnancy losses of unknown causes as well as 100 control samples of normal fertile women having at least one healthy child. The general aim of our study was to determine whether there is a relationship between genetic changes in the SYCP3 gene and recurrent pregnancy loss in human or not. Frequency of the heterozygous genotype and mutated allele C were significantly higher in women with recurrent pregnancy losses (P-value < 0.005). Our findings suggest that the T657C polymorphism of the SYCP3 gene is possibly associated with recurrent pregnancy loss of unknown cause in human.