AIM: To examine the expression of MMP-9 and TIMP-3 mRNA during choroidal neovascularization (CNV) in a murine model and to investigate the role of them in the development of CNV. METHODS: CNV was induced in C57BL/6J mice by intensive diode laser (810nm) photocoagulation (120mW, 75μm, 0.1s) of the fundus whereafter eyes were enucleated at 1, 3days, 1, 2, and 4 weeks. The MMP-9 and TIMP-3 mRNA expressions were analyzed using in situ hybridization and image analysis system. RESULTS: Both expression of MMP-9 and TIMP-3 mRNA had dynamic changes. For MMP-9, the expression was 1, 2, 4 wk>3d>1d (P <0.05), whereas TIMP-3 mRNA, 3d, 1, 2, 4 wk>1d (P <0.05). CONCLUSION: The imbalance between the changes of MMP-9 and TIMP-3 may accelerate the degrading of extracelluar matrix, and then be involved in the pathogenesis of CNV.