Abstract: The third generation of aromatase inhibitors (AI) play an important role in the adjuvant treatment of hormonal positive postmenopausal breast cancer. Compared with tamoxifen, either upfront or sequential using of Al can both significantly improve the outcome of breast cancer patients. However, there is a continuous debate of sequence or upfront usage of Al in clinical applications. With the publication result of BIG 1-98 clinical trial and interpretation of the data, we can further recognize and optimize the usage of Al in breast cancer treatment.