The Activating transcription factor 3 increases the cell survival, growth and immunity tolerance in body. Moreover, STAT3 is active as an oncogene and its high expression is reported around 70 percent of solid and bloody tumors. It is likely to increase expression in breast cancers, and this increase in the expression of STAT3 gene may be helpful in early diagnosis of breast cancer. First, HRRT1 gene was selected as a control gene, and then the condition of STAT3 gene expression was studied in 30 samples of malignant tissue and 10 samples of normal tissues using the Real Time PCR technique. Increased expression of STAT3 gene was seen in 26 out of 30 samples using the Real Time PCR technique. Among all STAT family members, STAT3 is often associated with tumor genesis and is considered as an oncogene. In general, STAT3 turned to the active form in a wide range of tumors in the cell, and especially, the structural activity of STAT3 which is reported in different types of tumors including multiple myeloma, lymphoma and leukemia, prostate cancer, ovary cancer, melanoma, kidney cancer, and colorectal cancer. In this study, STAT3 gene expression has a considerable expression in the malignant tissue of women with breast cancer compared with the expression of the same gene in normal breast tissue, and it can be considered as a prognosis and biomarker.