Abstract : Background: Tamoxifen is drug choice for female breast cancer in both pre and postmenopausal women as adjuvant treatment for hormone sensitive breast cancer. CYP2C19 play important role in the formation of a proportion of tamoxifen metabolites, including the conversion of 4-OH-TAM to endoxifen. Objective: in order to study the prevalence of CYP2C19*3 (G > A, rs4986893) and CYP2C19*17 (C > T, rs11188072) genetic polymorphism and their impact on tamoxifen therapy response in Iraqi breast cancer woman. Methods: This study was across-sectional observational study carried out at Imam AL-Hussein Medical City/Oncology center in kerbala and laboratories of College of Pharmacy / University of Kerbela, during the period between (November 2021 and Augest 2022). The study was conducted on total 100 females Iraqi women with (ER and /or PR) positive breast cancer who are taken tamoxifen (at least since 3 months). After taking blood sample from each patient genomic DNA was extracted from each blood sample by using the protocol and manufacturers instruction of Favorgen Bio Tech /China for blood genomic DNA extraction kit. Results: The mean age of participants in this study wass (51.08) years old. The distribution and percentage of individuals having ((C > T, rs 11188072) differ from those expected under Hardy–Weinberg equilibrium {number of observed vs expected were: CC (71, 63.2); TT (12, 4.2); CT (17, 32.6) (goodness-of-fit χ2 for rs 11188072; 22.891, P < 0.001} and therefore it was statistically significant. The distribution and percentage of individuals having (G > A, rs 4986893) differ from those expected under Hardy–Weinberg equilibrium {number of observed vs expected were: GG (20, 10.6); AA (25, 45.6); GA (25, 43.9) (goodness-of-fit χ2 for rs 93 18.507, P < 0.001} and therefore it was statistically significant. Conclusion: For this cross sectional study in Iraqi breast cancer woman, we observed that genotypes frequencies of CYP2C19*3 (G > A, rs4986893) and CYP2C19 *17 (C > T, rs 11188072) be consistent with Hardy–Weinberg equilibrium and the results were statistically significant and wild type (CC) of rs 11188072 and hetrozogyous (GA) of rs4986893 are more predominant genotype in these population . Key words: Breast cancer, Tamoxifen , CYP2C19 gene.