The jellyfish Catostylus tagi was studied as a food source. C. tagi is an abundant and unexplored resource of the Southwest Portuguese coast. The umbrella and the oral arms were separately assayed. Inorganics, nitrogen, and lipid content were estimated, being identified the major mineral, amino acid and fatty acid (FA) components. The scavenging capacity of C. tagi aqueous extracts fir hydroxyl (HO center dot), superoxide anion (O-2(center dot-)) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals were investigated, as well as their ferric ion reducing antioxidant power (FRAP). Both, tissues presented acceptable levels of heavy metals for seafood with mercury and lead not being detected. The contents of boron, taurine, and polyunsaturated fatty acids (PUFA), together with the in vitro capacity to quench HO center dot, have shown that C. tagi is polentially interesting for human consumption as well as for the production of specialty ingredients for the manufacturing of aquaculture feeds.