Keratoconus is characterized by progressive corneal thinning and protrusion, resulting in irregular astigmatism and visual impairment. Numerous studies show that matrix metalloproteinases(MMPs)play a key role in matrix degradation and thinning process. Corneal crosslinking(CXL)is a recently developed noninvasive treatment method which can delay or even prevent progression of keratoconus. Most studies focused on effect of CXL on corneal biomechanics and structure, but less on MMPs. Researches have shown that MMPs in tears of patients with keratoconus after CXL change, however alterations of those in corneal matrix remain unclear. Further study on the changes of MMPs after CXL is helpful to understand pathophysiological processes of postoperative keratoconus and mechanism of CXL stabilizing course of keratoconus.