Polysaccharides from seaweed have been shown to present a variety of antitumor effects, however the understanding of which structural patterns are responsible for these biological effects are still unclear. This review aimed to gather and critically evaluate published data of seaweed polysaccharide's chemical structure elucidation and their relation with antimelanoma effects. Data were collected at the electronic article databases Science Direct, NCBI/Pubmed and Google Scholar, selecting papers with polysaccharide structural information and biological effects on melanoma models. Most of the papers referred to sulfated polysaccharides as fucans and fucoidans, and to a lesser extent galactans, rhamnans, alginates, and neutral one's glucans. Fine chemical features as presence and position of sulfate groups, monosaccharide composition, linear or branched backbones, and glycosidic linkage type are crucial to antimelanoma effects, as well as molecular weight and macromolecular conformation. Display omitted