X-box binding protein 1 (XBP1), as a transcription factor, plays pivotal role in unfolded protein response (UPR), which is activated in response to endoplasmic reticulum (ER) stress to restore ER homeostasis. IRE1α/XBP1 pathway is a key component of UPR, and the expression levels of XBP1 can dictate the fate of cells under ER stress, either promoting survival or driving apoptosis. High expression of XBP1 in breast tumors is closely associated with poor prognosis. The paper elucidates the biological functions of XBP1 and its involvement in UPR, while also surveying the latest research on how XBP1 influences immunity, metabolism, apoptosis, angiogenesis, and the invasive and migratory behaviors of breast cancer cells. Moreover, it contemplates the potential of XBP1 as a therapeutic target for breast cancer treatment.