Breast cancer is the most prevalent cancer in women. Chemotherapy is the main strategy in the treatment of this disease especially in the advanced form of the disease. Despite the recent progress in the development of new chemotherapy, the effectiveness of these drugs has dramatically reduced due to multidrug resistance. The phenotype of multidrug resistance (MDR) can occur through different mechanisms as hereditary or acquired in response to chemotherapy, and could affect successful treatment of patients. In this study, we review the molecular mechanisms involved in multidrug resistance in breast cancer.