Objective:To observe the effect of intense pulsed light (IPL) on collagens and PCNA expressions in mouse skin and elucidate the biological mechanisms of photorejuvenation. Methods:Mice were irradiated on their right sides of the back with IPL(32 J/cm2),and their left sides were selected as control areas. At day 1,7,14 and 28 after treatment,skin specimens were taken at treated and non-treated areas,respectively. Histological and collagens changes were observed by hematoxylin-eosin-staining and Van Gieson staining. In addition,the expression of PCNA was investigated by immunohistochemistry at day 28 after irradiation. Results:Compared with non-treated regions,dermal thickness of treated regions had no significant change at day 1,7,14 and 28(P > 0.05). Collagens staining were stronger in treated regions than in non-treated areas at day 14 and 28(P < 0.05). The expression of PCNA also increased at day 14 and 28 after irradiation in treated areas(P < 0.05). Conclusion:IPL can enhance the content of collagens and also can increase the expression of PCNA in mouse skin.