The prevalence of breast cancer is rising worldwide. Irisin is a novel myokine that is proteolytically processed from the product of the FNDC5 gene. The study aims to assess the possible association of FNDC5/irisin gene polymorphism (rs3480) with the development of breast cancer. This study included 50 breast cancer patients and 50 healthy females matched for age as a control group. All subjects were submitted to full history taking, general clinical examination, pathological and radiological examination for grading and staging of the tumor, and laboratory investigations including CBC, Liver function tests (ALT, AST, serum albumin, serum bilirubin), lipid profile (TC, TG, LDL, HDL), Serum levels of CEA and CA 15–3 and genotyping of rs3480 (A/G) gene polymorphisms. There was a significant statistical difference between the two groups regarding the genotype frequency of FNDC5 (Irisin precursor) rs3480 (A/G). Regarding rs3480 (A/G), there was a high frequency of AA genotype and A allele among the control group. In contrast, GG genotype and G allele had the highest frequency among the breast cancer patient group. Multivariate analysis reveals that elevated cholesterol OR (1.312) (1.008-1.709), TG OR (1.074) (1.028-1.123), and GG genotype OR (5.052) (1.182-53.646) are significant risk factors for breast cancer. Conclusion: Our results indicate that GG genotype and G allele of rs3480 (A/G) polymorphism could be a risk factor for breast cancer