To clarify the mechanism of long-term repetitive UVA irradiation in photoaging of the skin, we evaluated albino hairless (SKH: HR1) mice by the irradiation with UVA (300-420nm) for 12months. The output of irradiated UVA was 30J/cm2/day. Skin samples were taken from each group and examined at 0, 4, 8 and 12months. Morphologically, the structural changes of elastic fibers were observed in the dermis of irradiated group. In immunohistochemistry, tropoelastin, matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase (MMP9) were expressed in the fibroblasts in the dermis of photoaged skin. The expressions of tropoelastin, MMP2 and MMP9 mRNA in cultured fibroblasts were analyzed by RT-PCR. The expression of MMP9 mRNA was increased cultured fibroblast derived from irradiated mice. These results suggest that MMP9 is an important mediator in the development of photoaged skin for one-year repetitive exposure to UVA.