The sulfated polysaccharides (SPs) from three macroalgae species were tested for structural and chemical characterization such as sulfate, carbohydrate contents, Fourier Transform Infrared spectroscopy , total phenol content (Folin-Ciocalteu assay) and free radical scavenging activity. The inclusion of the SPs (1000 mg/kg) as oil stabilizers in Oncorhynchus mykiss viscera oil in order to replace BHT was also assessed by analyzing oil oxidation indices (peroxide value, p-anisidine value, total oxidation value, free fatty acids and color changes) under 18 days at 65 °C. The yield, polyphenols and antioxidant potential of the SPs derived Sargassum boveanum and Padina distromatica were higher than Caulerpa sertularioides . Fourier Transform Infrared spectra results represented the existence of sulfate functional groups in all extracted SPs. The fish oil containing Sargassum-derived SPs reflected better oxidation indices. The SPs possess appropriate antioxidant properties, among which those extracted from S. boveanum , represented the acceptable results for conserving viscera oil, which is suggested as an alternative for the synthetic preservative. • Sargassum boveanum -extracted sulfated polysaccharides can be considered as a natural antioxidant. • The sulfated polysaccharides represented the acceptable results for conserving fish waste oil from oxidation. • The phenolic content and functional groups in sulfated polysaccharides induce high antioxidant potential.