Recently, marine-extracted sulfated polysaccharides (SPs) have been the subject of myriad research since they are considered an eco-friendly source of biologically active compounds. Meanwhile, food and pharmaceutical industries are in urgent need to produce natural sugar substitutes and antioxidants as alternatives to synthetic ones which are associated with cytotoxicity and safety issues. This study assesses the potential of using marine SPs obtained via the ultrasonic-assisted extraction of different marine species, to utilize them as antioxidant sugar substitutes. The carbohydrate, total phenolic contents and antioxidant activities, were measured for the SPs extracts of the algal species of Ulva lactuca, Jania rubens and the marine plant mangrove Avicennia marina. These SPs were structurally elucidated by Fourier Transform Infrared (FTIR) spectroscopic and high-performance liquid chromatography (HPLC) analyses. The results revealed that a highest yield percent of SPs was obtained from Ulva lactuca, 5.50 ± 0.25 %. The SPs of Avicennia marina had the highest carbohydrate content, 44 ± 1 % and antioxidant activity, 78.85 ± 0.06 at the 100 μg/mL concentration and 89.50 ± 0.21 at the 250 μg/mL concentration. Meanwhile, the highest phenolic content was exhibited by algal SPs obtained from Jania rubens, 132.60 ± 2.50 mgGa/g. Results also showed that the antioxidant potential of Jania rubens and Avicennia marina can be owed to their high glucose content. This work emphasizes the need to consider sulfated polysaccharides from marine sources for their antioxidant activity and to correlate it with their monosaccharide content to determine the effect of reducing sugar concentration on the antioxidant activity.