Natural polysaccharides from algae have gained increasing attention for their biological activities and potential for applications in food, pharmacology, medicine, and biology fields. This study aimed to investigate the effects of the Viscozyme enzyme on the polysaccharide extraction from Sargassum oligocystum algae. Then, the obtained polysaccharides were purified by using the Sevag method and Sephadex G-75 gel filtration chromatography before evaluating the antioxidant and antibacterial activities. The results show that the obtained polysaccharide was 2.06 ± 0.027 mg/g based on dry mass after extraction and the obtained purified polysaccharide with a purity of 76.28%, which was determined via the UV-Vis and FT-IR spectra with characteristic peaks. Antioxidant capacity of polysaccharides from S. oligocystum algae by DPPH and ABTS free radical scavenging tests with IC50 values of 4.90 ± 0.09 ppm and 4.01 ± 0.03 ppm, respectively. The antioxidant capacity of the obtained polysaccharides by Ferric Reducing Antioxidant Power (FRAP) and reducing powder (RP) with OD0.5 values were 3.52 ± 0.10 ppm and 0.27 ± 0.01 ppm, respectively. The antibacterial ability of the obtained polysaccharide was the concentration-dependent manner in the surveyed range of 200-1000 ppm via the antibacterial diameter of Escherichia coli (7.02± 1.01 mm to 13.33 ± 2.08 mm) ˃ Bacillus subtilis (4.67 ± 1.15 mm to 12.00 ± 1.73 mm).
