Matrix metalloproteinases (MMPs), also called matrixins, function in the turnover of extracellular matrix components. These enzymes are considered to play important roles in embryo development, morphogenesis and tissue remodeling, and in diseases such as arthritis, periodontitis, glomerulonephritis, atherosclerosis, tissue ulceration, and in cancer cell invasion and metastasis. All MMPs are synthesized as preproenzymes and most of them are secreted from the cells as proenzymes. Thus, the activation of these proenzymes is one of the critical steps that leads to extracellular matrix breakdown. This review describes recent progress made to elucidate the activation mechanisms of pro-matrixins which include extracellular stepwise activation common to most proMMPs, cell surface activation of progelatinase A and procollagenase 3, and intracellular activation of prostromelysin 3 and pro-membrane-type-1 MMP.