Objective：To explore the molecular mechanism of Toll-like receptor（TLR） 9 in ultraviolet B（UVB）-induced photoaging model of HaCaT cell. Methods：This experiment contains three groups：control group，model group，A151 group. The control group was given sham irradiation. The model group was established by the dose of 30 mJ/cm2 UVB irradiation. The A151 group was given the dose of 30 mJ/cm2 UVB irradiation and treated with TLR9 inhibitor. The cell senescence was evaluated by aging related beta-galac－tosidase cytochemistry staining. The cell proliferation rate was measured by CCK-8 assay. The contents of TLR9 and phosphorylation nuclear factor-κB（pNF-κB） were detected by Western blot. The mRNA expression of tumor necrosis factor-α（TNF-α） and inter－leukin-6（IL-6） were detected by RT-PCR. Results：The protein expressions of TLR9 and pNF-κB were higher in model group than control group（P=0.000，P=0.000），which were attenuated by the A151 treatment（P=0.010，P=0.000）. The mRNA levels of TNF-α，IL-6 increased in model group compared to control group（P=0.000，P=0.000），which were ameliorated by the A151 treatment（P=0.000，P=0.030）. The number of positive cells in aging related beta galactosidase staining was increased in model group than in con－trol group（P=0.000），while the number of positive cells was decreased in A151 group than in model group（P=0.000）. The cell prolif－eration rate of model group decreased markedly compared with that of control group（P=0.010），while the cell proliferation rate increased in A151 group than in model group（P=0.045）. Conclusion：The decrease of UVB-induced HaCaT cell prolifer－ation rate and senescence are mediated by phosphorylated nu－clear factor-κB and elevated mRNA of TNF-α and IL-6 via activation of the TLR9.