Textile dyeing industrial wastewater needs simplified and efficient treatment method for dye removal. Coagulation is a technique among several treatment techniques available for the removal of color in the textile effluent. In coagulation process, inorganic metal salts such as alum, ferric chloride, and synthetic polymers are generally used as a coagulant. Because of the drawbacks involved in metal salts, more research is motivated on natural biopolymeric materials. In this study, an efficient novel biopolymeric coagulant alginate, which is extracted from the Sargassum sp., a marine brown alga from the coastal region of Gulf of Mannar, is used for the removal of Reactive Magenta dye in the real-time textile industrial wastewater. The Reactive Magenta dye present in the wastewater is treated using the conventional jar test with alginate as a coagulant. The raw alginate and dye loaded alginate was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy techniques. The effect of alginate dose, calcium dose, and settling time was investigated. It was observed that the maximum color removal of 92.7% at optimum conditions of 30 mg/L of alginate dose, 4 g/L of calcium dose, and in a neutral pH was achieved. Based on this study, it has been validated that the alginate, a natural biopolymeric compound extracted from brown algae Sargassum sp., can be used an effective coagulant for Reactive Magenta dye removal from the real-time textile wastewater. © 2018 Desalination Publications. All rights reserved.