The changes in the translational repression and variation in mRNA degradation induced by micro RNA are important aspects of tumorigenesis. The association of microRNA-21 with clinicopathologic features and expression of programed cell death 4 (PDCD4) in Iraqi female's with breast tumors has not been studied. MicroRNAs were extracted from a set of 60 breast tumor tissues and blood samples of females with breast cancer and benign breast lesions obtained after breast-reductive surgery, and only blood samples from 30 normal volunteers. These extracts were evaluated for miR-21 expression by quantitative RT-PCR. Analysis of PDCD4 protein expression was carried out as miR-21 target gene by immunohistochemical tests and correlating the results with patients' clinicopathological features. Significant overexpression of miRNA-21 was found in breast cancer group. The fold increase in the miR-21 gene expression was significantly higher in circulating exosomes and breast tissues of breast cancer patients as compared to other groups (P \ 0.001). Overexpression of miR-21 was also significantly associated with the advanced tumor stage and histological grade. In breast cancer patients, PDCD4 protein expression was decreased to about 70% of the level in the control group. The delta Ct of exosomal and breast tissue miRNA-21 was negatively associated with PDCD4 expression. In conclusion, the translational repression of the PDCD4 induced by the high expression of miR-21 promotes breast cell transformation and development of breast tumor, and circulating miR-21 level could be applied to the screening panels for early detection of women breast cancer.