Abstract: [Abstract] Objective：To investigate the effect of UVB irradiation induced the matrix metalloproteinase (MMP-9) and Tissue inhibitor of Matrix Metalloproteinase (TIMP-1) mRNA expression on immortalized human keratinocyte cells (HaCaT cells)．Methods：Culture the HaCaT cells ,Draw cell growth curve, and the cells was treated with different doses (0、30、60、90 mJ/cm2)of UVB irradiation ,MTT method for determining cell proliferation.Semiquantitative-PCR (RT-PCR) was used to measure the expression levels of MMP-9 mRNA and TIMP-1 mRNA in HaCaT cells．Results：With the UVB irradiation accumulated, There was a decrease in the proliferation of HaCaT cells and an increase in the inhabation ratio, and there were significant differences in the values of OD (P < 0.05).The expression levels of MMP-9 mRNA increased,Comparative differences between groups were statistically significant(P<0.05).The expression levels of TIMP-1 decreased,There were significant differences in compare with0 mJ/cm2(P<0.05). Conclusion：UVB irradiation can induce the injure and apoptosis of HaCaT cells , MMP-9 and TIMP-1 maybe have some role in the pathogenesis of skin photoaging．

Key words: ultraviolet rays, keratins, photic stimulation, skin aging, matrix metalloproteinase 9, tissue inhibitor of metalloproteinase-1