Seaweeds are notable in producing diverse kinds of polyphenolic compounds with direct relevance to cosmetic application. This investigation was done to assess the bioactive properties of a brown macroalga, Sargassum siliquosum J. Agardh. This study is useful for improved utilization of S. siliquosum extract as a source of polyphenolic compounds important for the development of novel skin-lightening ingredient for the formulation of cosmetic products.