To investigate mechanism of mycosporine-like amino acid from Prophyra against ultraviolet irradiation-induced photoaging of skin and provide an experimental basis for clinical application of sunscreen cosmetics, MAAs derived from Prophyra haitanensis was extracted using hot water and the components of MAAs were separated and identified. The protective effects of MAAs on photoaging were observed by the degree injury of tissue appearance and pathological section. The protective mechanism of mycosporine-like amino acid from Prophyra against ultraviolet irradiation-induced photoaging of skin was measured by the activities of total superoxide dismutase(T-SOD), glutathione peroxidase(GSH-Px) and the levels of malondialdehyde (MDA)and hydroxyproline (Hyp). The results indicated that two major mycosporine-like amino acid components from Prophyra were separated: Porphyra-334 and shinorine. MAAs could prevent skin photoaging induced by ultraviolet irradiation. Compared with the control group, MAAs treatment group external inunctum exhibited significantly enhanced activity of T-SOD and GSH-Px, increased levels of Hyp, and reduced levels of MDA. But the groups of MAAs treatment external inunctum on antioxidant showed that it couldn’t have significant action compared with MAAs group gastric lavage . The mycosporine-like amino acid from Prophyra could protect skin from ultraviolet irradiation-induced skin photoaging.