Sargassum vulgare was sampled by free dives in Iskenderun Bay, Hatay, Turkey, in September 2018. Sargassum vulgare is a material with high economic value because it has compounds that can be used in medical applications such as alginic acid and at the same time it contains carbohydrates and vitamins. Alginates were extracted with a sequential extraction protocol from Sargassum vulgare. Structural characterization of alginate obtained from Sargassum vulgare was determined by FT-IR spectrum, phase structure by XRD diffractometer, and surface morphology by SEM image. Within the scope of the study, alginate obtained from Sargassum vulgare and herbal preservative 705 used in the field of cosmetics were compared. After pretreatment of Sargassum vulgare with ethanol, alginate extraction was performed. Microorganisms of Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, Escherichia coli, Aspergillus brasiliensis were used to examine the antimicrobial activity of the obtained alginate and showed that the contamination risk was tolerable for all microorganisms examined on the seventh day of incubation. Alginate obtained from Sargassum vulgare was found to be more effective than herbal preservative 705 at 0 hours. Pseudomonas aeruginosa, Staphylococcus aureus are microorganisms with the highest effect in the 0 hour. Since alginate obtained from Sargassum vulgare is more effective on microorganisms in a shorter time than herbal preservative 705, it is predicted that it can be a product that can be used in the field of cosmetics.