Abstract: Matrix metalloproteinases(MMPs) are the main enzymes for the degradation of the extracellular matrix(ECM).which facilitate the dissociation of epithelial cells from surrounding tissues.Previous findings have shown that MMPs are upregulated in both breast cancer and peripheral stromal cells.Recent studies show that MMPs may have great effects on the initiation of the epithelial-mesenchymal transition(EMT) in breast cancer.MMPs have also been found to act synergistically with many kinds of molecules, such as adhesion molecules, growth factors, and transcription factors, which can regulate MMP-induced EMT.MMPs have been investigated as potential targets for cancer therapy.However, clinical trials using MMP inhibitors have produced disappointing results, due in part to the lack of specificity and serious side effect.In this review, the authors provide a summary of the relationship between MMPs and EMT in breast cancer, and show how MMPs could cooperate with other functional molecules in the initiation of EMT.A deeper research may provide a new way for the prevention and therapy of breast cancer.