Abstract: Taking Porphyra haitanensis as raw material, we extracted the mycosporine-like amino acids (MAAs) and charaterized them by UV Vis spectroscopy and Liquid Chromatograph-Mass Spectrometer (LC-MS), so as to study the effects of various factors in the cosmetic system (pH, light, temperature, preservatives, antioxidants and functional additives) on the stability of MAAs. The results show that Shionrine and Porphyra-334 were the main MAAs in P. haitanensis. MAAs had the highest stability in the weak acid environment with pH=6. UV irradiation for 10 h could decrease the absorbance value by 94.4%. After having been placed at 48 ℃ for 56 d, its absorbance value decreased by 28.3%. At 48 ℃, the addition of small peptide and hyaluronic acid increased the absorbance value of the solution by 82% and 18.6%, respectively, which could improve the stability of MAAs compounds significantly. Other commonly used preservatives, antioxidants and functional additives had no significant effects on the stability of the MAAs.