Endogenous estrogen is currently considered a major risk factor for postmenopausal breast cancer. Under the catalysis of various enzymes, estrogen interacts through multiple metabolic pathways to produce various metabolites. The imbalance of estrogen and its metabolites in the body can induce physiological changes that may play a dual role in the development of breast cancer. However, due to the relatively low estrogen levels in postmenopausal women and the limitations of existing measurement methods in terms of specificity, accuracy, and reproducibility, the precise role of different estrogen metabolic pathways and their metabolites in the etiology of postmenopausal breast cancer remains unclear. Therefore, a deeper understanding of the estrogen metabolism pathways and their metabolites in the occurrence and progression of postmenopausal breast cancer may provide new insights for its prevention and treatment. Here, the authors review recent research progress on estrogen metabolism and postmenopausal breast cancer.