Proteolytic enzymes comprise five classes depending on their catalytic mechanisms: serine, cysteine, aspartic, threonine, and matrix metalloproteinases (MMPs). Proteases play an important role in all stages of cancer progression :cancerogenesis, invasiveness, and metastasis. Level and activation of proteases is associated with progression of breast cancer. Cathepsins are proteases involved in tumor formation, and activity of Cathepsin D (CatD) is considered as an independent tumor marker for breast cancer patients. Processes of apoptosis, cell proliferation, growth, angiogenesis, and metastasis are enhanced by CatD. MMPs represent a family of proteases that are involved in processes of invasion and metastasis through cleavage of basement membrane and remodeling of extracellular matrix. Considering that breast cancer had highly aggressive biology, it has been investigated and found that high activity of MMPs, particularly MMP-2 and MMP-9, is engaged in all stages of tumor progression. As proteases are involved in physiological processes such as immune response and in pathological conditions, it seems that examinations of molecular pathways of breast cancer could define a therapeutic target based on proteases.