In this study, the chemical composition and antioxidant profile of five edible macroalgae,Fucus vesiculosus,Palmaria palmata,Porphyra dioica,Ulva rigida, andGracilaria gracilis, cultivated in fully controlled closed systems, were determined. Protein, carbohydrates, and fat contents ranged between 12.4% and 41.8%, 27.6% and 42.0%, and 0.1% and 3.4%, respectively. The tested seaweeds presented considerable amounts of Ca, Mg, K, Mn, and Fe, which reinforce their favorable nutritional profile. Regarding their polysaccharide composition,Gracilaria gracilisandPorphyra dioicawere rich in sugars common to agar-producing red algae, andFucus vesiculosuswas composed mainly of uronic acids, mannose, and fucose, characteristic of alginate and fucoidans, whereas rhamnose and uronic acid, characteristic of ulvans, predominated inUlva rigida. Comparatively, the brownF. vesiculosusclearly stood out, presenting a high polysaccharide content rich in fucoidans, and higher total phenolic content and antioxidant scavenging activity, determined by DPPH and ABTS. The remarkable potential of these marine macroalgae makes them excellent ingredients for a wide range of health, food, and industrial applications.