Brown seaweed contains many biologically active ingredients such as fucoidan, alginate, phlorotannin (polyphenol), iodine, and laminarin with antioxidant, antibacterial, cancer cell inhibition and anti-ageing properties. Sodium alginate is present in large quantities in brown seaweed and is used to prepare low molecular weight polyguluronate sulfate, a substance with diverse biological activities used in medicine and functional foods. This study uses physical and chemical methods in chemistry to study the preparation of alginate from brown seaweed and low molecular weight polyguluronate sulfate from alginate. The results of preparing alginate and low molecular weight polyguluronate sulfate from the brown seaweed Sargassum have been summarized in the current study. Gel chromatography exhibited the molecular weight from 10 kDa to 60 kDa for polyguluronate sulfate. Alginate and low molecular weight polyguluronate sulfate was prepared. The results will be the basis for the production and commercialization of alginate and low molecular weight polyguluronate sulfate and their application in pharmacology and functional foods.