Matrix metalloproteinases （MMPs） are a group of zinc-dependent proteolytic enzymes able to cleave all major protein components in the extracellular matrix during the processes of wound healing and tumor formation. Tissue inhibitors of MMPs （TIMPs）， which exist in the human body， can regulate the activity of MMPs. According to different sources， MMP inhibitors are divided into TIMPs， natural MMP inhibitors and synthetic inhibitors. The classification and functional features of MMPs and MMP inhibitors are summarized and the relationship between MMPs， MMP inhibitors and posterior capsular opacification （PCO） are reviewed.