This study’s objective was to evaluate the chemical characterization and biological activities of sulphated polysaccharides isolated from Grateloupia catenata. The sulphated polysaccharide yield was 28.71±09%, with carbohydrate, protein, ash, and moisture content of 92.05±32%, 0%, 21.08±06%, and 4.03±29%. Carbon, hydrogen, nitrogen, and sulphur content of the sulphated polysaccharide were determined to be 33.07±21%, 4.21%±05, 2.15%±38, and 3.98±15%, correspondingly. The polysaccharide’s functional group was investigated using FT-IR. The sulphated polysaccharide demonstrated commendable antioxidant activity such as DPPH radicals, ABTS radicals, superoxide radicals, and hydroxyl radicals’ activity were 18.31–71.38%, 20.73–70.01%, 19.81–72.01%, and 18.72%–73.22% at the concentration of 50–250 μg/ml. Sulphated polysaccharide’s anticancer action against the A549 cell line was 21.98–70.41% at the concentrations of 50–250μg/ml. The results show that the sulphated polysaccharide exhibits strong antioxidant and anticancer action. As a consequence, the sulphated polysaccharide from G. catenata may serve as a food supplement, a natural antioxidant and anticancer, or as an ingredient in the pharmaceutical sector.