Abstract: Background and Objective: Breast cancer is the type of cancer that most affects women around the world. It accounts for around 30% of all cancers. KRAS gene is mutually initiated in about 20% of every single vigorous cancer. However, the further development of clinically successful KRAS coordinated malignancy treatments was usually unsuccessful and KRAS mutant malignancies are among the most resistant drugs. KRAS gene variations usually occur in many adenocarcinomas such as; lung, pancreas, breast and colon. The role of oncogene KRAS in later periods of neoplastic development that is taken after the onset is still poorly understood. The aim of this study is to investigate mutation and mRNA expression level of KRAS in breast cancer patients by using DNA sequencing and semi-quantitative reverse transcriptase techniques. Materials and Methods: The study included 44 paired normal and tumor samples from patients grouped based on the types of breast cancer and the patients' clinical characteristics, including age and grade of tumors. Results: The KRAS expression on the level mRNA was significantly increased (up-regulated) in tumor samples compared to the control samples. However, a heterozygous mutation (G>A) (GGT/GAT) was identified in two patients in the KRAS gene. Conclusion: The up-regulated expression of KRAS on the level mRNA can be a risk factor for breast cancer development and the changed KRAS expression level can alter individual breast cancer sensitivity.