In this study, we characterized the bioactive properties of three important brown seaweed species,Sargassum thunbergii,Undaria pinnatifida, andSaccharina japonica, by subcritical water extraction (SWE), as these species are well known for their beneficial health effects. Their physiochemical properties, including potential antioxidant, antihypertensive, and α-glucosidase inhibitory activity, and the antibacterial activity of the hydroysates were also analyzed. The highest total phlorotannin, total sugar content, and reducing sugar content in theS. thunbergiihydrolysates were 38.82 ± 0.17 mg PGE/g, 116.66 ± 0.19 mg glucose/g dry sample, and 53.27 ± 1.57 mg glucose/g dry sample, respectively. The highest ABTS+and DPPH antioxidant activities were obtained in theS. japonicahydrolysates (124.77 ± 2.47 and 46.35 ± 0.01 mg Trolox equivalent/g, respectively) and the highest FRAP activity was obtained in theS. thunbergiihydrolysates (34.47 ± 0.49 mg Trolox equivalent/g seaweed). In addition, the seaweed extracts showed antihypertensive (≤59.77 ± 0.14%) and α-glucosidase inhibitory activity (≤68.05 ± 1.15%), as well as activity against foodborne pathogens. The present findings provide evidence of the biological activity of brown seaweed extracts for potential application in the food, pharmaceutical, and cosmetic sectors.