Eutrophication caused by high nitrate levels in surface and subsurface water bodies is a major ecological concern. This process leads to the proliferation of algae and aquatic plants, which results in a reduction of dissolved oxygen and harm to aquatic organisms. Therefore, it is crucial to explore effective methods to remove nitrate ions from wastewater. In this study, the efficacy of Sargassum polycystum macroalgae as a biosorbent for nitrate ion removal was examined. The experiment investigated the impact of pH variations, initial biomass of S. polycystum algae, initial concentration of nitrate ions (50-300 mg L-1), and contact duration on the nitrate removal process. The dried powder of S. polycystum algae was used in the experiment. The findings indicate that the seaweed S. polycystum has a high capacity to absorb nitrate ions from wastewater, with a maximum absorption capacity of 545.70 mg g-1 of seaweed. The optimal test conditions for nitrate removal were found to be pH of 6, initial biomass of 0.02 g L-1, initial concentration of 300 mg L-1 nitrate ions, and contact duration of 60 minutes. Under these conditions, the nitrate removal rate was 52.8%. The results of this study suggest that S. polycystum macroalgae has a high potential for removing nitrate ions from wastewater. Overall, the use of S. polycystum as a biosorbent for nitrate removal can offer a cost-effective, eco-friendly, and efficient solution for mitigating eutrophication. Manuscript profile