This study was carried out to determine the main pigments in some different selected seaweeds and to reveal their antioxidant potential regarding the ever-increasing demand for utilization of marine pigments in human health and nutrition. The individual amounts of algal pigments were found by reverse phase high-performance liquid chromatography (HPLC) and their total antioxidant capacities (TAC) by two spectrophotometric TAC assays, namely: CUPRAC (CUPric ion Reducing Antioxidant Capacity) and ABTS/TEAC (2,2′-azinobis [3-ethyl benzo thiazoline-6-sulfonate])/(trolox equivalent antioxidant capacity). These two tests gave the same rank order for TAC. The TAC of HPLC-quantified compounds accounted for a relatively much lower percentage of the observed CUPRAC capacities of seaweed extracts, namely ranging from 11 to 68% for brown, from 4 to 41% for red and from 3 to 100% for green species, i.e., some TAC originated from chromatographically unidentified compounds. Fucoxanthin, chlorophyll a, and pheophytin a compounds were major pigments in brown algae. The relative carotenoid contents in red marine algae were generally lower than those of chlorophylls. Overall total quantities were quite low compared with those of brown species. In general, chlorophyll a and chlorophyll b were chiefly present in green algae, but β-carotene, violaxanthin and siphonaxanthin were also detected substantially higher in some species of green algae such as Caulerpa racemosa var. cylindracea and Codium fragile.