Background: Skin aging consists of photoaging and intrinsic aging. It is characterized clinically not only by rhytides, but also by pigmentary alterations and facial telangiectasias. There continues to be a growing interest in the efficacy of intense pulsed light (IPL) devices in the treatment of skin aging, as well as further defining its mechanism of action. Objectives: The objective of this clinical trial was to evaluate the effects and the mechanism of action of an IPL by comparing clinical photographs and biopsy results before and after treatment. Methods. A total of 58 patients were treated using a new IPL device. Clinical photographs were taken before treatment and compared to those taken 3 weeks after the treatment. Also, 4 cases had pathological analyses of tissues that were stained by haematoxylin-eosin and Uana orcein. Immunohistology of human collagen of types I and 3 and quantitative analyses of elastin and collagen were performed by a poly-functional digital image tight microscope; a transmission electron microscope was used for 2 of the cases to look for additional changes. Results: After 3 treatments, 62.1 % of the patients showed improvement in wrinkles and skin texture. Pigmentation improved in 84.6% of the patients, and a reduction in telangiectasis was seen in 81.25% of the patients. Pathological examination showed that both type I and type 3 collagens increased following treatment, but elastin content decreased; however, the elastin fibers were arranged more neatly. In the transmission electron microscope study, the amount of fibroblast activity increased, the fibroblasts were more active, and there were more collagen fibers neatly rearranged within the stroma. Conclusion: Clinical and pathological studies demonstrated that the IPL was effective in improving wrinkles and skin texture. The mechanism of action may be through the increasing activity of the fibroblasts, hyperplasia of the fibroblasts, and rearrangement of both collagen and elastin within the stroma.