The seaweed Sargassum occurs in large beds along Brazilian Coast, mainly in Southern and Southeastern areas. This seaweed is very important to local fauna and flora. It is also economically important mainly due alginate to production. Several kinds of approaches are needed to planning its sustainable management. This work aims to evaluate the size of subtidal Sargassum cymosum beds in Armação do Itapocoroy Bay (Penha, SC), quantifying its spatial variations on biomass and associated seaweed community, and also evaluate alginate yield separately for vegetative and reproductive branches, for each bed. The Sargassum beds area in Armação do Itapocoroy Bay reached 14,137 m2. Total estimated biomass in the bay was 17.90 ± 9.07 ton wet mass. Mean biomass ranged from 142,64 (± 34,25) to 214,76 (±131,68) g dry mass m-2 between the beds. The alginate yield ranged from 18.63 to 25.00%, and reproductive branches yield was higher than vegetative branches yield. Reproductive structures alone yield about 30%. Despite many additional works are needed, these results indicate potential for Sargassum exploitation in Santa Catarina Coast.