Objective: The diminished ovarian reserve (DOR) is a condition characterized by a reduction in the number and/or quality of oocytes. This primary infertility disorder is usually accompanied with an increase in the follicle-stimulating hormone (FSH) levels and regular menses. Although there are many factors contributing to the DOR situation, it is likely that many of idiopathic cases have genetic/epigenetic bases. The association between theFMR1 premutation (50-200 CGG repeats) and the premature ovarian failure (POF) suggests that epigenetic disorders ofFMR1 can act as a risk factor for the DOR as well. The aim of this study was to analyze the mRNA expression and epigenetic alteration (histone acetylation/methylation) of theFMR1 gene in blood and granulosa cells of 20 infertile women.Materials and Methods: In this case-control study, we analyzed the mRNA expression and epigenetic altration of the FMR1gene in blood and granulosa cells of 20 infertile women. These women were referred to the Royan Institute, having been clinically diagnosed as DOR patients. Our control group consisted of 20 women with normal antral follicle numbers and serum FSH level. All these women had normal karyotype and no history of genetic disorders. The number of CGG triplet repeats in the exon 1 of theFMR1 gene was analyzed in all samples.Results: Results clearly demonstrated significantly higher expression of the FMR1 gene in blood and granulosa cells of the DOR patients with theFMR1 premutation compared to the control group. In addition, epigenetic marks of histone 3 lysine 9 acetylation (H3K9ac) and di-metylation (H3K9me2) showed significantly higher incorporations in the regulatory regions of theFMR1 gene, including the promoter and the exon 1, whereas tri-metylation (H3K9me3) mark showed no significant difference between two groups.Conclusion: Our data demonstrates, for the first time, the dynamicity of gene expression and histone modification pattern in regulation ofFMR1 gene, and implies the key role played by epigenetics in the development of the ovarian function.