Abstract: The human gastrointestinal tract is inhabited by numerous microbes, which form a vast microbial community that could protect the body from invading pathogens and promote immune system development and the absorption of nutrition. An imbalance in the gastrointestinal microbiome might contribute to various illnesses including inflammation and tumors. Worldwide, breast cancer is the most frequently occurring cancer and seriously threatens female health. The gastrointestinal microbiome could regulate the metabolism of estrogen and function of immunity. Previously, a study suggested that the clinical and pathological features of breast cancer are appreciably associated with the imbalance of the gastrointestinal microbiome. In this review, we focus on the latent correlation between the gastrointestinal microbiome and breast cancer, expecting to provide some novel viewpoints in understanding breast cancer. This would be beneficial for better management of breast cancer.